Are you seeing this?

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://deb.torproject.org/torproject.org bionic InRelease: The following signatures were invalid: EXPKEYSIG 74A941BA219EC810 deb.torproject.org archive signing key

If so, do this:

sudo apt-key adv \
--keyserver keyserver.ubuntu.com \
--recv-key 74A941BA219EC810

…which is deprecated (etc, etc) but worked for me.

Source