Hello,
I wrote a document a while ago to install pglister, pgweb and pgarchives that might help you, although your setup is
notexactly the same:
https://gitlab.com/cmatte/pglister/-/blob/master/INSTALL.md
I guess you're missing the part where you have to create a community auth site in pgweb's
/admin/account/communityauthorg/add/and /admin/account/communityauthsite/add/
Good luck,
--
Célestin Matte