Yeah it was a headache for me in the past too, but the latest Steam Big Picture which behaves more like a Steamdeck has made it pretty easy. Since it launches right away, I can easily launch and quit steam games with 0 issue and when I’m done I used big picture to just shut the PC down.
One issue I found was if I let the PC sleep, it always brings up the login screen on wake so I just shut it down everytime. NVME’s are so fast the boot up is whatevs. Non-steam games are also a little painful as sometimes it won’t switch active windows, or I have to login or something.
I only use this machine for games. Like you said, HTPC was a pain. I have a different server that I have Plex setup on and I use Apple TV’s / Roku’s for streaming.