I dunno, i am usualy upgrading my instance i didn’t do any install from scratch for long time.
Unit peertube.service not found seems really to indicate that something is missing in systemd configuration.
At least it should fail.
Do you have a file peertube.service withn /etc/systemd/system ?
What does it contains ?
a sample can be found within var/www/peertube/versions/peertube-v2.0.0/support/systemd/peertube.service ( yep i din’t yet installed latest v2.1.0 ).