I thought the Supremes had been hiding in a different universe?
Regardless, any way to safely pass to other galaxies at all should be thoroughly avoided for the time being. The point of this sequel was to avoid the issues from before, and part of that was eliminating the possibility of intergalactic empires. There is no rate of growth here that will consume the huge number of planets in the milky way any time soon. The moment we end up with nations large enough to need to move to other galaxies is the moment one can well and truly declare the sequel a failure with no reservations. Considering that, collectively, we don't even hold 200 planets should prove we don't need to move to another galaxy at all any time soon.
If people aren't going to fight to get the resources they need then tough luck, they can perish. That's how it is, no deus ex machina to make the other galaxies reachable/habitable is coming in the foreseeable future, so everyone needs to adapt or die.
No one should be holding even a hundred planets for at least two dozen more pages, I think we're good for now