Update:
I determined that the /etc/exports: Operation not permitted lines above were due to the fact that iTerm, my command line app did not have full disk access. I followed these steps
(https://github.com/hashicorp/vagrant/issues/10234#issuecomment-424305964) to grant that app full disk access in macOS’ Security & Privacy settings, which fixed this issue for me.
This thread can now be closed out.