Raspberry pi 3 b+ plex media server REaLLy Work for you?

Plex Media Server Desktops & Laptops
2

Please review my official instructions and the discussed limitations. Anything else is not supported here at all.

Also, with PMS on your RPi it is crucial that EACH of your devices supports Direct Play or Direct Stream. Nearly no armv7 or armv8 PMS server has the CPU to transcode 1080p+ video.

https://support.plex.tv/articles/200250387-streaming-media-direct-play-and-direct-stream/