There are 2 versions of the Windows/Mac app.
Keyboard/Remote Big Screen type Plex HTPC - #10 by Moussa
and
Plex for Windows which has made it to the download page: https://downloads.plex.tv/plex-desktop/1.43.3.2951-1d73e3f3/windows/Plex-1.43.3.2951-1d73e3f3-x86_64.exe
Most browsers are exclusively h.264. That 1080p HEVC Main 10 format you have, while valid is not widely supported by the clients.
