I was in a meeting yesterday with someone whose background was, I think, large random triangles in shades of white and light grey, but it could have been an attic room with sloping ceilings. That seems optimal: a plain background which is plausibly architectural but not identifiable.

Or, take a picture of what the wall behind you would look like if you were in the office? Presumably you'd be disguising WFH rather than being in the building.

Or take a picture of your most impressive bookcase and then fuzzify it so people can't see the details, if you're misleading people who don't know what your office looks like.

But be careful not to trust this too far: https://www.youtube.com/watch?v=dX7AyuCE1FE