> it'll show you the age of satellite imagery, if it's available

Thanks for this tip, I've used iD quite a lot and I never knew about this. Unfortunately few of the images have their vintages labeled.

The Bing Aerial is Oct '22, which is pretty recent. I suspect it's the most recent. I see it as a rectangular (covered) pool, but the circular shape in the NE corner is throwing me off. Might be a hot tub with intersecting geometry? Might be an open pool umbrella? Who knows.

The Esri World Imagery has a clearer, rectangular pool that matches what I thought I saw in the Bing image. Since this pool appears to be installed into the ground, I feel fairly confident it's a newer installation.

Esri World Imagery (Clarity) Beta and Mapbox Satellite both show the oval, above-ground pool that you describe. In my experience these are usually both older than the other satellite image sources, but there are always exceptions.