I'm using Lakka-Switch.L4T.aarch64-2.2-devel-20190728151829 from the lakka site. This was the "latest" stable from a year ago. Is there a new one?
As for psx emulator I'm using the pcsx rearmed one
And as for SD I'm using a SanDisk ultra micro sd. With 100MB read speed. Yes it's a U1 but reading is 100MB. (tested with a copy from SD 85MB per second)
I know it's confusing, but yes there's a new build. Read the more recent posts in the thread and there's a link to it, a user here has compiled it, It's from May2020. PCSX rearmed is the proper core to use. If you're still having issues after this let me know and I'm happy to help.