Based on some posts I saw on the PWM_Sensitive Reddit I'm trying the OnePlus Pad 2. I'm not sure if it's "perfect" (have only used it for a short period of time) but it's much better than anything remotely modern that I've tried.
For background I can't seem to use anything "new" right now and iOS updates beyond iOS 15 or 16.1 make even Apple LCD's unusable for me. Updates on Windows 10 as of around May 2024 gives me symptoms on previously perfect machines and I can't seem to find anything on Windows 11 that works.
So I'm pretty sensitive and the One Plus Pad 2 definitely seems to be better than a lot of other options.