I HAVE THE FIX! After many many attempts (and a few long and circular AI chatbot threads which never seemed to help) I have now achieved what was thought impossible: Davinci Resolve now can open, load existing project, display video, play audio and do everything it should!
Turned out that whatever OpenCL I had was not OpenCL I needed. So I ran yay -S opencl-amd , removed the conflicting packages and now It’s totally fine!
I mean, you still have to replace libs from this thread and do the whole
cd /opt/resolve/libs
mkdir _disabled
mv libgio* libglib* libgmodule* libgobject* _disabled
but afterwards it totally works, which is amazing to me. Managed to find that the combination of AV1 video and PCM audio from FFmpeg imports just fine. This is huge, I will now actually look into getting Studio version forr all the codec support and other features.