RX 6400 and LG C5 Oled

[cybermat]

Hello, i read very old posts about LCD and Groovymame, so i didn't resume them.
First of all, i know how to use Groovymame with LCD, because my bartop is equipped with a fixed 60 hz monitor.

Since i own a Freesync LG C5 Oled monitor, i can use it with vrr with no issues at all, but the question is using it with custom resolutions.
If i would like using it WITHOUT VRR, adding custom resolutions from 50 to 61 hz, is there a way to use Groovymame and let decide to it the best resolution?

If i put LCD under monitor i'm locked to the one in use and under logs i see that all the other resolutions are locked.

I would like using baddudes at 57 or mortal kombat at 54, i know that are not precise but are better than 60.

Could you please guide me to do this? I use win11 and amd rx 6400. Thanks