Sidecar resolution won't reset

[japtor]

Little background to my setup, Monterey 12.2.1 (and a version or two before) on Intel, with 2560x1440 display and sidecar on iPad mini (2021).

Not entirely sure how this happened, but started when I started messing with BetterDummy. Basically with BD not running and/or reset and everything, Sidecar runs 2560x1440 on the iPad. Only with a BD virtual display connected (even before mirroring the BD display as in the normal use case), the iPad runs as it normally did before (something like 800p). This has lasted through restarts and OS updates.

Not a huge deal since BD works great, but I kinda have to use it for Sidecar to be usable now.

[waydabber]

Are you sure it's 2560x1440 and not 2266x1488 (which is the standard resolution of the mini)? If the latter, then you can change this back to 1133x744 (the same resolution with HiDPI enabled) in macOS.

[waydabber]

One caveat though - the option to change the resolution won't come up by default in macOS, only when you mirror the Sidecar display to some other display and choose that other display to change the resolution. This is not logical but this is how it is. This works this way without BetterDummy so the app does not need to be running.

[japtor]

(Replying to the first post first) There's no option to change resolution of the Sidecar display that I've ever known of, at least on my setup...which is why I was playing with BetterDummy in the first place. Double checked with System Info:

Sidecar Display:
Resolution: 2560 x 1440 (QHD/WQHD - Wide Quad High Definition)
UI Looks like: 2560 x 1440 @ 60.00Hz
Framebuffer Depth: 24-Bit Color (ARGB8888)
Main Display: Yes
Mirror: Off
Connection Type: AirPlay
DELL U2515H:
Resolution: 2560 x 1440 (QHD/WQHD - Wide Quad High Definition)
UI Looks like: 2560 x 1440 @ 60.00Hz
Framebuffer Depth: 30-Bit Color (ARGB2101010)
Display Serial Number: FJYC775S0D5L
Mirror: Off
Online: Yes
Rotation: Supported
Adapter Type: DVI or HDMI
Automatically Adjust Brightness: Yes
Adapter Firmware Version: 2.19

Then after opening BD with a dummy but before mirroring:

Sidecar Display:
Resolution: 2266 x 1488
UI Looks like: 1133 x 744 @ 60.00Hz
Framebuffer Depth: 24-Bit Color (ARGB8888)
Mirror: Off
Connection Type: AirPlay

And to the caveat, yeah just found that. I was wondering if it's just some macOS bug I'm running into or not cause of that. The 2x option doesn't come up here but yeah, the 1133x744 does. Seems I can mirror at that resolution but that's it, once I stop mirroring and go back to extending it reverts to 1440p.

[waydabber]

Hmm. Honestly I have no idea how did you achieve that. The Sidecar display matches the display's resolution it is mirrored from, but without mirroring it should revert back to the native resolution which is 1133x744 or 2266x1488 depending on what was last used.

Anyway, you can clear all display related stuff by removing com.apple.windowserver.displays.plist from under /Library/Preferences and your user's Library/Preferences/ByHost folder (here there might be multiple files like this with some UUID-s attached to the filename - clear them all) and then reboot.

[japtor]

Haha yeah no clue. Closest I can figure was I think switching the iPad to the main display on accident once and panicking (figuring all my windows would be jacked up) and quickly switching back. I had BetterDummy running at the time and trying to get that going that but forget the details beyond my own messing things up there.

In any case, yeah getting rid of those plists did the trick, thanks. Didn't have /Library .displays plist but saw a bunch of displays in the .windowserver only one so just got rid of that.