When I worked in an office, the “own time” and “own equipment” were pretty much the same, I would work at night at home on my side projects.
Now, with remote, the “on my own time” is more blurry. The OP mentions the they can deliver code quickly. I understand that they could fully deliver what their peers, bosses, PMs, company expected in less than 40 hours a week. And that would free them time to work on their project if not for the IP clauses. On a job without that IP clause, I imagine no one will care if they were working on their own project at 3pm if by 2pm they already delivered what is expected for the day.
In my case, I usually work on my own projects in the morning, sometimes I start a little bit late, but I get the job done and all is good.
It's definitely more blurry now but I think there was a blur without remote work too.
For example, you might work at an office and come home but then think about a programming problem you had at work at 9:30pm. Not so much sitting at a code editor but your mind is occupied with the problem and potentially you even solved it on paper so you can output the code tomorrow "at work".
Or maybe during your lunch break you're mentally churning through some problem you were stuck on 2 days ago because that's how your brain operates.
This is why the idea of working long blocks of set hours is so strange to me in this field. I often solve very complex problems when talking a walk, showering, nearly falling asleep or the second I wake up. None of this is "on the clock time" in a traditional 9-5 job but very important work happens during these after hour times -- often times it's uncontrollable because your brain has actively running background tasks that finish when they want to finish.