Auto-update Plex Server on Linux

I just stole the entire text from Plex’s web site:

DEB-based distros (Ubuntu, etc.)
The PMS package will automatically do all repository setup for you on Debian 10+/Ubuntu 20.04+ installations, including obtaining the package signing key.

To enable use of the repository edit the last line of the file 

Find the line:

#deb https://downloads.plex.tv/repo/deb/ public main

To use the repository, simply change this line to remove the comment character # and save the file

deb https://downloads.plex.tv/repo/deb/ public main