A lot of old school maker projects are fun, but they're also basically E waste making kits now that phones do almost everything.
Not having a bunch of low tech gadgets laying around is really nice, they can easily become the biggest clutter challenge in a space, the same way paper used to back when more people still used it for things other than books.
Building a small solar energy system is fun and easy, and also practical.
3D printing is fantastic.
Meshtastic has a lot of DIY and learning potential and is like the lite edition of ham radio. What's really cool is that range testing gets you outside.
Maybe design something together with JLCPCB and have it made(Leave off any through hole connectors and solder them yourself for both fun and pretty decent cost savings).