The LD_DEBUG environment variable (2012) (bnikolic.co.uk)

LD_AUDIT is another one worth knowing about (though I admittedly use it less often than LD_DEBUG) https://man7.org/linux/man-pages/man7/rtld-audit.7.html

Used this once to debug an issue where it turned out unwanted exports in one library A where used to satisfy imports in another library B and thus preventing library A from being unloaded. Fun times.

The ldd command is also essentially just a wrapper script that sets LD_* variables that get the dynamic loader to do all the real work.