This function is quite complicated on Linux:

        def find_library(name):
            # See issue #9998
            return _findSoname_ldconfig(name) or \
                   _get_soname(_findLib_gcc(name)) or _get_soname(_findLib_ld(name))

_findSoname_ldconfig() uses "/sbin/ldconfig -p" and searchs for 'libc6,x86-64' in the output (on x86-64).

_findLib_gcc() uses "gcc -Wl,-t -o tmp -lc" command and search for "lib" in the created "tmp" file.

_findLib_ld() uses "ld -t -lc" command and searchs for "lib" pattern.

The exact code is more complicated :-) You should debug this issue by running these commands manually on Debian.

Note: python3.9 -c 'import ctypes.util; print(ctypes.util.find_library("c"))' commands displays libc.so.6 with Python 3.8, 3.9 and 3.10 on Fedora. I cannot reproduce the issue on Fedora 33 (x86-64).