This is what I’ve done done to launch PMP on startup on my Raspberry Pi 4.
Open a terminal, and execute the following commands to create an autostart directory (if one does not already exist) and edit a .desktop file. (Everything between the —> <— arrows. Sorry, just wanted to get this out there without spending a while figuring out formatting.)
—>
mkdir /home/pi/.config/autostart
nano /home/pi/.config/autostart/plexmediaplayer.desktop
<—
Copy in the following text into the plexmediaplayer.desktop file
—>
[Desktop Entry]
Version=1.0
Name=Plex Media Player
GenericName=Media Player
Comment=View your media
Exec=plexmediaplayer
Icon=plexmediaplayer
Terminal=false
Type=Application
Categories=AudioVideo;Video;Player;TV;
Actions=TVF;TVW;DesktopF;DesktopW;
[Desktop Action TVF]
Name=TV [Fullscreen]
Exec=plexmediaplayer --fullscreen --tv
[Desktop Action TVW]
Name=TV [Windowed]
Exec=plexmediaplayer --windowed --tv
[Desktop Action DesktopF]
Name=Desktop [Fullscreen]
Exec=plexmediaplayer --fullscreen --desktop
[Desktop Action DesktopW]
Name=Desktop [Windowed]
Exec=plexmediaplayer --windowed --desktop
<—
Should work perfectly. Good luck!