This issue seems to affect Plex when used on Android TV media streamers like the 2019 Nvidia SHIELD Pro, and even on Android Smart TVs like the Sony Bravia.
Burn-in is a big issue with OLED technology. And it occurs when the TV shows a picture that is static for an extended period of time. What happens is you will see a faint image of the burned-in image, even when the screen changes or shows a blank screen.
For some reason, Plex chose not to show a screen saver when playing music. Instead, the picture is static, with no movement making an OLED television all the more susceptible to burn-in.
This occurs when using Player Version: Plex for Android TV 8.11.0.22186 and Plex really needs to do something to make this app either run a screen saver or play a short video in a loop even would help.
Just something to be careful about, because Santa may have brought you a new OLED TV for the holiday, and you will want it to last as long as possible. Because this technology still is not cheap. Plus, manufacturers won't cover screen burn-in under warranty, so it's something you will need to live with for as long as you own your OLED TV.
You can read more about screen burn-in here on CNET.
Other Music Apps To Use Instead of Plex
These Android apps will all let you play tons of music and Internet Radio stations:
AccuRadio
iHeartRadio
myTuner Radio
Pandora Radio
Radio Online
For more great TV apps for Android -- CLICK HERE