I think it's very rare, I've worked at Google for 8 years and I've met maybe 1 person who works from home on a somewhat regular basis.
A lot of the people I mentioned above actually transferred PAs to make remote work work. If that's a goal of yours, Google's a big enough company that there's probably a role available.
The problem is that you need a VP exception for remote work and many VPs don't believe in it at all. So there are entire orgs where the number of remote people is zero.