I don't understand, how could a company own your IP if you work outside of business hours on your own computer? Unless it's in direct competition with trade secrets of your employer's business I don't see how they could claim ownership over anything. They can't enforce ownership over generic things like writing a user management system, a billing portal or creating a searchable and sortable data view? Loosely related…
I've ran into this a couple of decades ago interviewing with the EA (Electronic Arts). The guy literally said that if you work "properly" for them, you will not have any time left for side projects or any such nonsense. But this seems to be more of an exception than a common thing. The vast majority of companies are far more reasonable. In some places (Cal?) your right for side projects (and the off-hours IP) even protected by the law.