1) Go to world with a mirror

2) Gaze into your soul

3) Resize the application window to be 3x width (arbitrary amount, but I have 3 monitors)

4) Gaze into your soul, now with less pixels!

5) Turn your head so you see your mirror reflection on the far edge of the app window while it's stretched across the monitors.

6) Gaze into your soul once again, now with MORE pixels!

I tried with different FOVs and both normal and high FOV exhibited the loss of mirror quality in the center of the app window in the extra-wide layout. This happens regardless of the Mirror Resolution specified on the component. Setting it to x1024 makes the differences more apparent than auto resolution.

Attached pics for proof (shown with x1024 res). Blurry is the app stretched across my three monitors, the other is full-screen on one monitor, stretched one captured on my left monitor while looking right in-game.

I would assume this might also affect users who are using an single extra-wide (probably curved) monitor as well. I don't have one so I cannot explicitly confirm that. I'd be curious if this would affect the rare extra-tall monitor setups as well...

UPDATE (since it still lets me edit the post wew):

I have been reminded of the mirror resolution graphics quality setting, and reminded that the default option FULL is not the same as the UNLIMITED option. Switching to Unlimited in the Graphics Settings solves the issue.

I believe this is more of an education/documentation issue than a technical one.

https://creators.vrchat.com/worlds/components/vrc_mirrorreflection/ this page is the only meaningful information I could find about specific mirror settings.

TL;DR please update the user graphics settings documentation, and include awareness about screen resolutions larger than 2048px having quality loss and that switching to Unlimited can fix the quality (at the cost of performance of course).