It only depends on your employment agreement in the other direction. Work done for hire is by default owned by your employer under federal law. For salaried employees it doesn't matter if it is done during working hours.
The employment agreement can give up this right for things not related to the company's core business, and I usually insist on that in my agreements. But that is not the default behavior.
I usually insist that personal and open source work done outside of the product areas I work on are not company owned. Otherwise if I work on financial software at a bank, and then at home I work on defi/blockchain based financial stuff, I could be setting up a liability for me or my users.
Now I understand what you are saying, and no. For a salaried employee it pretty much covers everything you do that is related to your job, with that “related to your job” being interpreted very loosely, or done with company equipment or on company time.
The employment agreement can give up this right for things not related to the company's core business, and I usually insist on that in my agreements. But that is not the default behavior.