Not as far as I know.

But maybe you can work around it. One way I can think of is to combine all the individual polys into one massive one using the CONTOURSM command. This will create a single polygon that matches the complete outline of the existing ones, and you now have a single poly to use the area command on.

I don't remember the screens in the installer for the Annual 2023 off the top of my head, but at least some of our products have a screen with a checkbox that enable you to do an "artwork only" install (for use without CC3+). I don't remember if the 2023 annual had this, but if it does, make sure to NOT enable that option during install, or it will only install the artwork for use with other software, and not the CC3+ components. Try rerunning the installer and see if this is the case.

Some of the more typical things people forget are map title and other labeling, scale bar and compass roses, and they forget to use proper scale for the map. For the latter, when using Info -> Distance, the value should be what is expected. For example, if measuring along the a scale bar, the value in the dialog should match the displayed value on the scale bar. If the measurement come up wrong, it is likely that the entire map is scaled wrongly. Or if it comes up right, but the values on the scale bar doesn't match your intended scale for the map, it also means it is scaled wrong.

It's not that I don't like buttons, it is just that setting up toggle switches is simply more work than just handle a straight-forward map. But generally, a map with toggles are preferable to having multiple maps of the same location. The linking system in the atlas is primarily designed to link different locations together, and doesn't work as well when linking two different versions of the same map together, primarily because there is no sensible way to indicate a linking spot on the map itself for that purpose, so it will only be in the sidebar (or below the map in the web version viewer)

Which color are you assigning them?

Based on your description, it sounds like you may have manually changed the palette for your map, and then assigned them this color. While there is technically nothing wrong with this, the palette in CC3+ can reset to the default map palette unless it has been properly re-attached to the map using :CC2PRESETS: after any change.

The recommended way to deal with Color Key is to give the entities Color number 6 in the palette, this is one of the default colors that appear in all official palettes, and shouldn't change even if a new palette is loaded or the current one is reset.