> But if I create things in my free time at home, on my own equipment, then that's MINE, and I might start a company from it

That's not entirely accurate: You're required to submit it to your employer if it could be related to your work, see especially §18 (1-2) and §19

https://www.gesetze-im-internet.de/arbnerfg/BJNR007560957.ht...