Generally, when an employer owns your "inventions", this only applies to "inventions" created while using the employer's resources. Most employement contracts will make it sound like they own every waking thought, but in most cases when this has been taken to court, the precedent has been set, that it really only applies to inventions or ideas that happen in relation to and using employer's resources.
So this means that an employer can argue they own software that you build:
- On a company-issued computer
- Using contacts you garnered through work
- On company time (this is complicated for salary employees, but definitely applies to time in the office, or standard business hours when you are expected to be working)
- Work collaborated on with other co-workers
Now I should clarify, I am not a lawyer. None of this is legal advice, yada yada...
But generally you can work on side projects and skirt around intellectual property clauses as long as you make sure to distinguish work time and work resources from your personal projects. The biggest thing is to avoid doing it while at work (or when expected to be actively working if you are remote), and avoid using a company computer or piggybacking off company resources (for example making a sub-account in your employer's CI/CD tool to run tests for your software).
So make sure you have seperate accounts for everything, avoid doing it on company time, and use a personal computer (not a work-issued computer) and you should be absolutely fine with working on a side project.