Perhaps the smoking gun that this is on Asobo's side is the problem doesn't exist in flatscreen...
Asobo made changes to object culling in SU5 and perhaps that affects mipmapping too. This was almost certainly motivated by PSVR2 on PS5 - and thus could explain the difference between flatscreen and VR.
The problem with complaining to Asobo is they'll most likely kneejerk blame it on the third party aircraft and I haven't seen it in first-party aircraft so it'll just get deflected back.
I have seen this exact behavior in one other aircraft: Taogs Hangar A365. One panel behaves exactly the same as what I see with the A/S indicator in the Baron; it's one or two mipmap levels lower than the rest of the cockpit, in VR only. I'm hoping they'll dig into it and find something that points a finger at something.
Note: aircraft are downloaded so it's not a streaming issue, rolling cache reset - just in case, dynamic settings off, foveated rendering off, off-screen terrain caching set to ultra - just in case.