your intel gpu is fine.
do you have subtitles and/or tone mapping enabled? if so, its possible that its going through the cpu.
tone mapping is currently cpu on windows, subtitles, and audio are all cpu single core processes.
disabling subtitles and/or tone mapping will help identify what is causing the problem(s).
other than, I think, safari, web browsers do not direct play hevc/265 in plex. so it is unlikely that your pc was direct playing.
what does the plex dashboard show you, it should indicate when (hw) ie gpu is being used for video decoding and encoding.
if the server is crashing, it sounds like either a driver or hardware issue (possibly overheating).
otherwise, without logs, its impossible to do anything other than guess.
to be honest, if you don’t have a 4k/hdr tv, there is not really much point to collecting 4k, you simply make it more difficult on yourself for doing so.
you may want to read the entire thread @ Plex, 4k, transcoding, and you for a lot of 4k discussion and background info.
