You just have to compile that specific supported version of gcc. On an earlier CUDA, I had to compile gcc-4.9. Unlike Debian, Fedora just seems to remove all traces of old packages.
They've come to the conclusion that you should also come to, that Fedora is basically a waste of time to support because whatever you've gotten working will be terribly broken in the next release for no good reason anyone can point to?
Edit: oh wait I think I see. Latest supported gcc for CUDA 11 is gcc 9.x, but I think latest Fedora is on gcc 10.