See if just opening the task manager and leaving it open also keeps the pc from freezing. If so - that points towards a malware.

Additionally you can set up a monitoring software to get the load readouts on your phone and see if maybe something weird is going on when the pc should be idle (like 100% cpu load or disk usage). Pitikapp + hwinfo is a free combination for such setup.

Does the keyboard numlock button change state when the pc is frozen (led turning on and off when you press it)?

It’s basically a self-hosted stream that moonlight connects to within your network. https://github.com/LizardByte/Sunshine/releases You still need any and all software that’ll actually be running on the server, but you can use sunshine either for streaming particular applications from it or just as a general all purpose remote access tool. So it’s like Parsec, only FOSS and imo works better too.

Switched to sunshine+moonlight from steam remote play. Works much better, especially on low end clients. And as a bonus you have full access, not just for steam.