OP’s question was about what he can use his RPi for now that he’s moved his Home Assistant setup off of it and to a mini PC.
It’s a good question, though a bit off topic for this forum. RetroPie is a good suggestion, but I’m honestly interested and curious to see what other suggestions are given here. I think starting with an RPi and eventually moving to something more powerful is a pretty common pathway for Home Assistant users, so I’m sure there are others wondering what they can utilize their RPi for now that it’s no longer needed for Home Assistant.
This also isn’t a general home automation forum, this is a forum for Home Assistant and things related to it. Any question about Home Assistant, and about using things with Home Assistant, is welcome here. We can’t help you with everything though
Magic mirror is a fun project and has hassio integration. Could also add some of the community scripts on there for presence detection like monitor or BT-mqtt-gateway.
I have 6 pi @home …
1 PI3b+ running Hass.io
1 pi2 running PiHole (adblock/dns/dhcp)
1 pi2 running motionEye OS (videosurveillance)
1 pi2 running recalbox
1 pi zero running PiClock
and 1 pi zero w running motioneye (mobile wifi camera … for baby room, cars, … etc …)
I think adding one for face recognition and one for offline vocal assistant (like jarvis, sarah …)
1: Pihole is a great addition to any lan. It is IMHO better kept separate to other service on your LAN because a DHCP/DNS server is absolutely fundamental to your whole IP network and should not be allowed to fail. Also you get local name resolution, both forwards and backwards. Of course there is a home assistant integration, just to keep me on topic. And a proper network setup will always assis home assistant.
2: Get a screen and make a nice control panel for your wall.
3: Make a weather station and integrate it with HA.
4: Put some relays on it and use it as a garage door opener, integrated with HA.
There are so many pi projects out there that if you cannot find anything to do with it, your google skills are failing you :). Most of the projects you will find are open source, so integrating them in some way, via rest, command line sensor or mqtt is, well, non trivial, but easily doable in most cases.
Let us know what you end up with
EDIT: media player, either squeezebox (audio) or kodi (video and audio) - both of which integrate with you know what…