Mac Slow When Using Sidecar With Your iPad? Here's What's Going On

Sidecar feels magical when it works — your iPad becomes a second display in seconds, no cables required. But when it’s misbehaving, the Mac feels heavier than it should, the cursor lags between displays, and your fans pick up for no good reason. The iPad shouldn’t be making your Mac slow. Often, though, it is.

What Sidecar actually does

Sidecar is doing real work continuously while connected:

1. Captures a portion of your Mac’s screen at high frame rate
2. Encodes it as H.264 or HEVC video in real time
3. Streams the encoded video to the iPad over Wi-Fi or USB
4. Receives Apple Pencil and touch input back from the iPad
5. Routes that input as if it came from the Mac
6. Maintains the secure connection between devices

Each of those is non-trivial. The encode in particular costs real CPU, and if the encoder is forced to drop quality to keep up, you get the laggy/blurry symptoms.

Free up RAM in one clickSweep frees inactive memory and pauses the processes hogging your CPU. Get Sweep free →

Test 1: Wired vs wireless

Plug the iPad into the Mac with a USB-C cable. Connect Sidecar over the cable. Use it for a few minutes. Then disconnect, switch to wireless, use it again.

Wired Sidecar:

• Lower latency
• More reliable connection
• Some Macs hardware-accelerate the encode better with USB
• Charges the iPad as a bonus

If wireless feels laggy and wired is smooth, your Wi-Fi network is the bottleneck. If both feel laggy, the Mac is the issue.

Fix 1: Use USB-C if you can

This is the single biggest fix. Wireless Sidecar shares your Wi-Fi bandwidth with everything else, and the encode quality has to drop to fit available bitrate. Wired Sidecar is essentially a dedicated channel.

If you’re using Sidecar for any extended period, plug in the cable. Battery on iPad lasts longer too.

Fix 2: Check Activity Monitor while Sidecar is active

Open Activity Monitor → CPU. Sort by % CPU. With Sidecar running, look for:

• WindowServer — significantly higher than usual (compositing for two displays)
• VTEncoderXPCService — the video encoder, expected to be working
• AirPlay XPC Helper — wireless connection management
• sidecar relay — connection daemon
• CommCenter — for cellular interactions if iPad has SIM

WindowServer at 200%+ during Sidecar use is normal-ish. WindowServer at 200%+ when Sidecar is idle (just sitting there as a second display showing nothing) is a problem.

Fix 3: Reduce what’s on the Sidecar display

The encoder works harder when there’s more motion and color complexity to encode. Things that make Sidecar work harder:

• Animated content (videos playing, GIFs)
• Lots of small text being scrolled
• Complex backgrounds
• Many moving windows

If you’re using Sidecar to dock a chat app or a music player, that’s light. If you’re using it to display Premiere Pro’s timeline scrubbing, that’s heavy.

Fix 4: Drop Sidecar to a lower frame rate (kind of)

There’s no explicit setting for Sidecar frame rate, but you can effectively reduce it by:

• Putting Sidecar in “extended” mode rather than “mirrored” — extended is lighter because it shows different content per display
• Not putting demanding apps on the Sidecar display
• Using Sidecar for static content like reference docs, chat apps, music controls

These aren’t toggles, but they shift load off the encoder.

Fix 5: Check the iPad

Sidecar requires both ends to be healthy. An iPad that’s:

• Low on storage
• Running iOS that needs an update
• Stuck on a bad Wi-Fi router
• Running other heavy apps in the background

…will struggle as a Sidecar display, and the Mac will work harder to compensate.

Restart the iPad before a Sidecar session. Close other apps on the iPad. Make sure it’s on the same Wi-Fi network as the Mac (some Sidecar issues come from devices on different SSIDs).

Fix 6: Update both devices

Sidecar is one of those features that gets meaningful improvements in nearly every macOS and iPadOS update. Out-of-date software is more likely to have known issues.

• Mac: System Settings → General → Software Update
• iPad: Settings → General → Software Update

Update both. The compatibility matrix Apple maintains works best when both ends are recent.

There’s a faster waySweep diagnoses what’s eating your performance and clears it in seconds. Try Sweep free →

Fix 7: Disable Sidecar features you don’t use

There are several toggles for Sidecar features that you might not need. With Sidecar active:

• The sidebar with quick keys (toggleable in Display Settings)
• The Touch Bar at the bottom (also toggleable)
• Apple Pencil double-tap shortcuts

Each adds some overhead. If you don’t use them, turn them off:

System Settings → Displays → click the Sidecar display → toggle off the parts you don’t use.

Fix 8: Check Wi-Fi quality

If you’re using Sidecar wirelessly and seeing lag:

• Hold Option, click the Wi-Fi menu bar icon
• Look at Tx Rate and RSSI
• Tx Rate under 200 Mbps will struggle for high-quality Sidecar
• RSSI worse than -70 dBm is too weak

Move closer to the router. Or switch to USB-C for the session.

Fix 9: Quit other heavy apps

Sidecar wants the GPU and the encoder. If you’re also running:

• Photoshop or another image editor
• A video editor with a timeline scrubbing
• A game in the background
• Multiple browser tabs with autoplay video

…you’re competing with Sidecar for resources. Close what you don’t need. Sidecar will breathe.

Fix 10: Restart the connection

Sidecar connections accumulate state. After hours of use, especially with the Mac sleeping and waking, the link can be in a degraded state where it works but slowly.

Disconnect Sidecar from the Mac side (Control Center → Display → click the iPad to disconnect). Then reconnect. Often this clears whatever was hung up.

The cleanup angle

Sidecar is one of the more sensitive macOS features when it comes to overall system state. A Mac that’s running tight on memory, has cluttered caches, or has many background processes feels noticeably worse with Sidecar than without. The cleanup wins:

• Free RAM (encoder needs working memory)
• Clean caches (so the system isn’t paging during Sidecar use)
• No leftover background processes from old apps
• Clear out old AirPlay/Sidecar metadata if you’ve used it with multiple iPads

Sweep handles all of this in one scan and shows you what’s about to be removed before doing anything. The speed boost feature also frees inactive RAM right before launching Sidecar — clean slate. Notarized by Apple, free to download.

Don’t restart — cleanSweep clears the buildup that’s actually slowing your Mac. No reboot needed. Free for macOS →

When the Mac is actually too old

Sidecar is supported back to fairly old Macs (2018 and later, generally). But “supported” doesn’t mean “great.” On 2018-2019 Intel MacBooks, Sidecar runs but always with some lag and noticeable thermal load. On Apple Silicon, it’s essentially free.

If you’re on an older Intel MacBook and Sidecar always feels rough, the answer might be using the iPad as a separate device (with apps that work standalone) rather than as an extended display. Apps like Notability, Procreate, and Numbers are great on iPad without needing Sidecar at all.

A pre-Sidecar checklist

For a smooth Sidecar session:

1. Plug in iPad with a known-good USB-C cable
2. Make sure both Mac and iPad are on the same Wi-Fi (even if using cable — Sidecar prefers it)
3. Quit unused apps on the Mac
4. Don’t put a video-playing window on the Sidecar display
5. Plug your Mac into power if on battery

Five seconds of prep that turns a flaky session into a smooth one.

Common Sidecar specific issues

Some patterns I’ve seen come up repeatedly:

• Sidecar disconnects every few minutes — Wi-Fi handoff issue, try wired
• Cursor lags between displays — almost always Wi-Fi, try wired
• Apple Pencil input is delayed — same, plus check Pencil battery
• Sidecar display is laggy but Mac display is fine — the encoder is the bottleneck, drop window contents to less demanding apps
• Sidecar cuts out when you take a phone call on the Mac — known issue with audio routing, accept the call on a different device or quit Sidecar first

When to give up and use Universal Control instead

Universal Control is the cousin feature where your Mac mouse and keyboard control the iPad, but each device runs its own apps. No screen streaming, no encoder load. If you don’t actually need Mac apps on the iPad’s screen — just need a cohesive desktop with iPad alongside — Universal Control is much lighter.

Both can be enabled simultaneously. They’re listed under Displays settings.