I've got a PC that my job was throwing out and I put a CPU, hard drive and RAM combo I got on Craigslist (that's like gumtree) for $20USD in there and I've only ever had problems with 4k and HDR. Plex itself is pretty cheap perf-wise! Transcoding can be a problem but you can set it up to pre-transcode multiple quality options or just stream it original quality if you have the bandwidth.

Linux is definitely malware. I installed it and I haven't been able to use my computer since