Force monitor to 30 HZ for VSR

[Rstudio]

Hello there.
I have a 4K monitor, 60 hz by default and am using a 7900 XTX GPU. I can select and play at 60 hz or 30 hz at native resolution ( 4K) and below.
Using VSR to play at higher resolution like 5K or even 8K, the refresh rate is locked to default 60 hz .
I can't find a way to force and use 30 hz with VSR, and i badly need it.

I tried several trick with the registry , but nothing worked for now.
Can someone help me with that ? Maybe by changing the default refresh rate of my screen to 30 hz instead of 60 hz, so that VSR uses 30 hz ?
I can pay a bit if needed.

Thanks a lot.