I’m getting the same issue on Raspbian GNU/Linux 10 (buster), see below (executed at 18:33 BST):
sudo apt-get install plexmediaserver -y
Reading package lists… Done
Building dependency tree
Reading state information… Done
The following packages were automatically installed and are no longer required:
libexiv2-14 libgfortran3 libgmime-2.6-0 libmicrodns0 libncurses5 libssl1.0.2 rpi-eeprom-images uuid-dev
Use ‘sudo apt autoremove’ to remove them.
The following packages will be upgraded:
plexmediaserver
1 upgraded, 0 newly installed, 0 to remove and 270 not upgraded.
Need to get 76.9 MB of archives.
After this operation, 13.6 MB of additional disk space will be used.
Err:1 https://downloads.plex.tv/repo/deb public/main armhf plexmediaserver armhf 1.22.3.4523-d0ce30438
404 Not Found [IP: 104.18.12.47 443]
E: Failed to fetch https://downloads.plex.tv/repo/deb/pool/plexmediaserver_1.22.3.4523-d0ce30438_armhf.deb 404 Not Found [IP: 104.18.12.47 443]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
