Just to confirm, neither HDR@89Hz nor HDR@91Hz work, but HDR@90Hz and HDR@65Hz do?
Also, you can disable Unified Frame Limit Management to revert to the older split slider config to be able to set sub-61hz locks without removing changes entirely.
I will likely make an update which changes things such that even values between 91 and 121 get skipped over, in order to avoid trampling over 46-60hz options from unified limiter which already work.
Signal padding, there happen to be empty/blank pixels sent which make things easier for display controllers when detecting timings, historically those blank pixels were there to give time for CRT electron beams to move to where the next line or frame began.
For BOE panels at 90hz, they receive frames which happen to be 858x1320 pixels in size, with an active area of 800x1280, while SDC panels use frames which are 1128x1312 in size, also with an 800x1280 active area.
So…
for BOE: 858x1320x90 = 101930400; ie a clock of ~101.93MHz; though in reality the panel runs at 102mhz so has a refresh rate of ~90.0615Hz.
and for SDC: 1128x1312x90 = 133194240; so a clock of 133.194mhz; but they run at 133.200MHz instead which gives a refresh rate of ~90.004Hz
Reducing how large of a padding area gets sent may be possible, but without having an SDC panel deck myself I’m not able to test to which degree, if any, that would be possible.