If you parents have a standard TV stick or Apple TV their devices support a variety of codecs.
This means that you can “direct stream” content from Plex / Jellyfin with minimal CPU impact.
At 1080p it should at least support ~4 direct streams when it doesn’t have to “transcode”.
That said, even if it is weak by today’s standards it’s a good platform to learn the setup on. Then you can move to something else more powerful (but still cheap) once you understand it all.
At least that’s how I did it, 3b+ -> Pentium J5040