This will probably get lost in the noise. But I think what sucks the fun out of side projects is where your agency is taken away by the ‘right way’ to do things. That’s what makes embedded and a lot of Raspberry Pi projects so fun. There isn’t a large collective telling you to use X build tool plus Y framework, and if you don’t, it’s because you’re doing a bad job and don’t care. And if you ask a question like ‘how do I…’, the response is Y takes care of that for you, you should really use Y.
Pick up an Arduino and there’s no one right answer. It’s still very hobby oriented, so a lot of people do fun an wacky things. The learning curve is fairly short. What I call the ‘book count,’ or how many books you need to read to be productive, is pretty low. On the other end of embedded, it gets very formal, very quick, but that’s for professional embedded developers.
Or, pick a ‘dead’ language. Go to some vendor like thrift books, or hunt used book stores, for books on that language. You might find some for $5. There’s no pressure, and you have full agency to make the greatest or the worst decisions you want. And a lot of the communities around these ‘dead’ languages are a lot of fun.