Did you restarted your phone after installation? I have a K20 Pro and on first boot and configuration gestures also didn't work. After a simple restart all was okay and have stayed okay since then.
There are a few bugs, to be expected, some visual details (fonts too big overlapping some sentences), also some animations stutter sometimes a little and font download on themes app gives an network error (although everything is fine with the network).
Dark mode still doesn't work ok with some apps that don't support it natevely (and with the ones that do support tries to change them also, looking weird on some cases).
Overall a good ROM, better than last MIUI 11 in my opinion.
I like the design changes made to MIUI 12...
Regards,
Vitor Correia
Enviado do meu Redmi K20 Pro através do Tapatalk