>looking for more ideas

1. MotionEye can help set your own local security camera setup.

2. PiHole with Unbound can help setup network wide ad blocking and DNS over TLS.

3. SDR (DVB-T dongle) with rtl_433 can receive 433Mhz communication from your sensors like Fire Alarm, Gas Sensor, Car key etc. and notify you.

4. MQTT server on a Pi can act as a local notification server, MQTT client on your phone can receive notifications.

Of course, the possibilities with a SBC are endless, but I included just those projects which I feel can be implemented without much effort but provides huge lifestyle/cost-benefit improvements.