I installed QGIS-3.34-1 from official repositories (extra). On startup, en error box pops up with the message: ModuleNotFoundError: No module named 'jinja2' . I could work with venv or conda to install missing package(s), however shouldn’t installation of packages from the official repository ensure that all dependencies are resolved?
I managed to close that popup and the main GUI did show up.
Its an Arch package … and it looks like its a known/open issue 
Thanks. This list will keep me going.
can you try to install jinja2 manually by using pip.