OK, after searching on the Tutor forums, I found this post and was able to use the commands:
tutor local run -v /home/tutor/all_course:/tmp/bla cms ./manage.py cms export_all_courses /tmp/bla
and
tutor local run -v /home/tutor/all_libs:/tmp/bla cms ./manage.py cms export_content_library library-v1:Org+LibName /tmp/bla
to successfully export things.
And then since I didn’t want to spend more time, I just wrote all my library names to a file and used xargs to invoke the library export command for each of them.