Cursor starts lagging over time during virtual display mirroring

[xezrunner]

I'm using a MacBook Air M1 with 8GB of RAM. My usual setup of BetterDisplay is:

• Connect external display (1920x1080@75Hz LoDPI)
• Turn off internal MacBook display
• Enable a virtual monitor (2560x1440 HiDPI)
• Mirror it to the external display

This works fine for the first couple of minutes. As I continue working, the cursor eventually starts to visually freeze (but logically still moving), then it becomes choppy, until I disable and re-enable mirroring.

Making the virtual monitor 1440p LoDPI or any other resolution also has this behavior.

This has been an issue on Sonoma as well, and is still an issue in the latest macOS 15.1 betas that I'm currently using.

Is this something BetterDisplay could have influence over, or is mirroring completely up to macOS?

[waydabber]

Mirroring is fully macOS. However virtual screen mirroring (same with Sidecar, DisplayLink etc) generally has cursor issues on Apple Silicon (fine on Intel) since macOS Monterey 12.4 (if I recall correctly). Apple never fixed these issues since then despite some pleas from the community.

[xezrunner]

Ah, good to know that it isn't just BetterDisplay being affected by this. Thanks!
I assume there are no workarounds for this at the moment, other than toggling the mirroring when this happens.

[waydabber]

Probably - but to be honest this specific cursor issue is atypical. Maybe it is caused by the difference in refresh rates (60Hz for virtual screen vs 75Hz for the display)? Make sure both run at 60Hz.

[xezrunner]

Setting the refresh rate to 60Hz only makes it less noticeable, but the cursor certainly still becomes visually laggy over time.
It also does happen even if I mirror the internal MacBook screen to the external display.

I have since discovered that with the "Enforce virtual screen mirroring" option turned on, I can click Stop mirroring and it'll do a quick stop-and-reconnect, fixing the issue if the lag becomes severe enough.

I have the external display connected through a dongle with HDMI, not sure if that's also something that could cause problems, but this to me feels like a software issue, likely on the macOS side.

[waydabber]

Hmm. If you mirror the internal screen to the external display, then it's not a virtual screen related problem. Interesting. Generally mirroring should work fine in macOS.