A GMT user posted an issue that I was able to reproduce in WSL2 + gcc9. The error is
ERROR: LoadError: LoadError: could not load library "/home/j/programs/lib/libgmt.so"
/home/j/programs/julia/bin/../lib/julia/libstdc++.so.6: version `GLIBCXX_3.4.26' not found (required by /usr/lib/libgdal.so.26)
Googling I found this SO post mentioning a fixed bug in gcc9 that might affect linking against objects built with gcc that had not that bug fixed.
As an experiment I moved away the julia/bin/../lib/julia/libstdc++.so.6
and GMT started to work. Ofc, this was just to test but the user told me that he built Julia master and the issue went away.
It’s strange that this does not affect more people, but it dis afffect two today.