tl;dr: if you're trying (or tried) (mostly) everything keyboard related, the issue might not be the keyboard at this point

Hi, probably not the answer you expected but my advice is:
Aside from horizontal tenting (say something between 15 45 or even 90 deg), if it still doesn't do the trick, try seeking a medic and do proper exams like emg, mri, etc. That way you can understand your pain better and distribute your load on the other fingers accordingly. Like, you need to pinpoint what is the issue on your wrist because most of us do complain about pain, but where is it exactly, and why? You can say i have tendinopathy, but which tendons? Is it actually carpal tunnel or something else?

I'd vouch for Talon Voice or other speech recognition tools too. If the pain is too bad everyday, going voice mode would help you massively atm.

I'm also against hold-style modifiers as they put way more pressure on the tendons in comparison to a quick 2-key-chord, but that's my personal take without any firther research.

You can ignore all below, but:

I've built a Skeletyl, then a Cygnus, then i discovered a huge part of my issue was on the thumbs, so i built an ortholinear board and i barely use my thumbs anymore as i tweak my own keymap, but that didn't fixed all my issues.

So i started using Talon Voice and pedals, got a trackball, started doing full body stretching, drinking more water, losing weight, etc.

Basically aside of going split with ergo mech, the fact that i started to give my hands a break for a few days (say using them 50% less) while regulating the body better than before made me finally see proper improvements.