Thank you!
Is that a new feature? I have over a thousand contributions on StreetComplete (casually using it during walks) and somehow I never noticed that button.
Sort of. It was added in 2023. (https://github.com/streetcomplete/StreetComplete/pull/5373)
The overlays are intentionally a bit hidden, since they're more of a power-user feature and I appreciate that StreetComplete retains beginner-friendliness as a core tenet. But the overlays are indeed awesome for survey-type walks where you just want to make sure that all sidewalks are mapped correctly, or to see which shops are still missing.