I got Retropie working flawlessly on pi4 using the method previously described in this article, but managed to accidentally ruin my image later, so I came back to the article and see that it has now been changed and I cannot get the new method to work. Following the steps, I cannot get the pi4 supported version as" git fetch && git checkout fkms_rpi4 " results in "permission denied" errors. I tried to use chown on the entire ./git folder, but just got messages that I do not have permission to use those operations, and my command line experience ends there, and I don't know what to do.
The old method just tricking the retropie into thinking you're a pi3 worked perfectly for me, but I cannot for the life of me figure out where you went to manually config the platform permanently, and the old article is no longer available, you have also blocked waybackmachine, so I cannot tell what you originally did. Could you please post the old method or let me know where to config the platform?