They had something like this when I worked at Atlassian, which was copied from Google (like most everything there)

You could pick a thing to work on outside your normal job and they’d “give” you time. However you had to basically justify it to your manager. This also hilariously ended up in having to plan OKR style achievements for your spare time project. So it was another, voluntary layer of micromanaging crap added over your real job.