I feel sorry to see you drowning on your own with no one giving you some help here ...
The GroovyArcade version you're using is hardly maintained by its author, hardly once a year, and it's really not updated. Anyway, this is what I can explain you :
- the AdvanceMenu is using a kernel built-in resolution, hardly any chance you can change it yourself unless you download the kernel sources, apply the 15kHz patch, and add your own timings. Why not, that's some advanced user resolution (in the case of kernel >= 5.6)
- the intermediate user answer is not that better either : you should create an EDID file based on the MK timings, add it to the initramfs, and change kernel parameters to not use the kernel resolution but instead force the screen EDID with the one you've built
- another possibility is to force the Xorg kernel resolution by editing the xorg.conf. That's probably what is already happening in VeS' GroovyArcade version, but this method is ... 10 years old, ad that's not how in 2020 things are supposed to be done. Anyway, you'd add/edit the required resolution timings. The easiest to do that is to find MK resolution + refresh rate, and use them with the switchres binary to compute timings.
No solution is easy. You may even end with a progressive resolution on your frontend, when an interlace one is much better. Well, that's the matter of personnal preference afterall