exploring GCC / GLIBC and compiling internals & How to switch between multiple GCC versions

How to switch between multiple GCC and G++ compiler versions on Ubuntu 20.04 LTS Focal Fossa:

Additional notes:

Amazingly cool, you can even patch an elf as a last resort (say you don't have the source code of a binary, but need to change the "runtime loader search" then you can do, using 'patchelf' from the nix project see