After posting this question, it occurred to me that it certainly appears that the likely cause of my issue is a mismatch between where the files and links are located on my system that don't match up with where "they are supposed to be," and possibly, though less likely, the contents of pertinent environment variables.
It would be great if there was some description somewhere of "where they are supposed to be", so that I can ensure my system conforms to what is expected.
So, in short, what is expected? For a normal, working installation, where are the files normally put, what are the locations for links to current versions of files, and what is expected of the environment variables and their contents?
Here, "modern Fedora" means (for me at least) Fedora 32 and 33, and version 10.3.1.1 of gcc, though surely this is quite stable over many versions.
I expect this is documented somewhere, but I have no idea where.
Thanks for your insights.