I am building electrical measurement equipment daily and tried to sell couple peripherals for Raspberry Pi as side project. The stupid thing is, that you don’t decide what’s in direct competition. That decides a lawyer and I got rejection since both were electrical systems :-))

It's not: See https://www.gesetze-im-internet.de/arbnerfg/__18.html You must report everything that is not clearly and obviously unrelated to an employers business. That's different from "direct competition". The circumstances under which an employer can make claims to it are more nuanced: If it's related to a field that the employer has business in or is preparing to have business in, they get a right of first buy for at least a non-exclusive license. And that's the problem with google: They do basically everything IT-related. Whatever you might invent - it will likely be related to field google is in or is preparing to be in.