I had the same urge i.e. do something physical but something that was still technical in nature and you could use it as hobby income.

I bought a laundromat 5 years ago. Learned to fix mechanical issues, troubleshoot electrical issues. Learned to use tools to pull bearings out, using heat torches to remove worn out sleeves from a shaft, understanding how water valves, solenoids works. Learnt a lot.

While it is not as crazy as building something new, it is the closest I could get to with my software engineer career. My friends thought I was nuts.