Best Miryoku firmware for a hand-wired, split, wired skeletyl

I built this lovely bastardkb skeletyl and initially used a bit with miryoku kmk. I noticed for whatever reason that sometimes the right side hung up and now after flashing the latest kmk it does not seem to work at all.

It is well soldered and I somehow believe it's really a kmk issue - followes all the rules for Split etc. I often also had little timing issues with the hold-tap behavior which is really non-existent on zmk and other boards for example.

Long story short: I am using waveshare's rp 2040 zero in here and would want to try out another firmware for miryoku. I will need to configure the board pins, it's hand-wired. What can you recommend to get it done with minimal effort?

QMK?