Hi Larry

You said...

Or are AIs the real intelligences of the galaxy and beyond and they
don't need no stinkin' Earth-type worlds to live on - except as material
to build their Dyson Shell "bodies" some day.

...which neatly intersects some ponderings I've been working on. Milan Cirkovic & Robert Bradbury postulated the "Migration Hypothesis" in which ETIs of Matrioshka Brain grade travel to the Galactic Perimeter to get better access to the Cosmic Heat-Sink. I've been working out the Galactocentric distances involved for given blackbody temperatures - approximating the Galaxy as a point source for my first rough run. For a 2.735 K flux the distance is 56,800 ly for a 3E+10 solar luminosity for the Milky Way.

But for warmer heat-sinks the Opik-Oort Cloud provides a natural "Dyson Shell" with lots of in-space resources ready-to-use. Seems like a natural habitat for ETIs too and nigh undetectable unless we're willing to watch for thousands of hours hoping for a transit.

FYI...
Temperature (K) vs Radii (AU)
35 127
30 172
25 248
20 388
15 690
10 1552
5 6209
4 9702
3 17248
2.735 20753

...neatly covering all the Inner O-O Cloud. Past 810 AU hydrogen should freeze if it's present. I think its vapour pressure (which is still 7 kPa at 13.84 K) will remain pretty high down to very low temperatures, so any body will still need serious gravity to hang on to it. Conceivably there will be Mars to Earth sized objects out there covered in hydrogen ice.