libidn2.so.0 no longer exists, it is now named libidn2.so.4.
Indeed. I filed: https://gitlab.com/libidn/libidn2/issues/63
If libidn2 upstream sticks with the new soname, I will write (and backport) code in glibc to deal with it.
It looks likely that the soname bump will be reverted.
The libidn2 soname bump was reverted upstream.