Same here with Mint 21.1 and Ardour 7.3.
After installing autotalent and rescanning plugins, there is an error when scanning it :
Cannot load module “/usr/lib/ladspa/autotalent.so” (/usr/lib/ladspa/autotalent.so: undefined symbol: __exp_finite)
That problem has come up with other packages, it occurred after a change to glibc. Try recompiling from source, linking with the newer version of glibc and libm on your machine may fix the problem.
Alternately you could ask your distribution maintainers to compile the plugins properly. Plugins should be statically linked so that they do not risk conflicting with host or OS libraries, so any problems with the linker finding symbols should be found at link time, not run time. I’m not positive, as I only dabble in software these days, but the fact that an error occurred at runtime attempting to locate an external symbol would seem to indicate the plugin was compiled with dynamic linking.