In my country, as a salaried dev, I can definitely get sued for copyright infringement if I decide to quit working for a company and open a competing business. Even if I didn't intentionally copied any code/asset the legal process by itself would be a hassle to deal with when I'm just starting a business and depending on how I decided to write my new stuff for my business I can indeed be found guilty because I unintentionally copied myself (same design decisions, using the same tech stack, variable naming convention, same price formula for... to the point that could be reasonable argued that I just copied and pasted some important portions if not the whole code base), so yeah, if I decided to do something like this I would quit before writing a single line of code for my business and probably take a vacation/work on something else for a few weeks, before jumping in.
yeah that's bullshit, you can own the IP you can't own what the employee knows about their field. that is just corporate overreach.
https://www.npr.org/2021/07/09/1014366577/biden-moves-to-res...
You can't have your cake and eat it, too. If you want to sell software, don't work for someone else in that business. Just sell it yourself!