I tried to install Debian 11 on an Early 2014 MacBook pro and it didn't have video at all for me in the installer. I didn't pursue it after that. You have done a lot to get this to work.

I've tried different Linux distros on this computer and Manjaro was the best out of the box that I tried. I recently changed to Arch thinking that it was the true source of Manjaro's working, and it is not so much. I've got it to an OK state though.