I would like to use the time for open source development. I get to learn and make things that would actually help people.
That said, I don't think I'd do it because of the risk of producing software that may be company property since it was done on company time and on company hardware.
I agree that's a risk. However you likely can do soft forms of development on company time such as reading documentation and code, pruning / responding to issues...
Additionally it's going to be hard to argue against(or sue) if you're improving a FOSS that your company depends on and benefits from a feature you add.
In the past I've used these kinds of situations for personal development. Linkedin learning, oreily, certifications, youtube tech talks etc.
No one has complained about it yet. /shrug