ok, I've been thinking this for a while now and are curious if anyone else thinks the same.
At the end of Rise of Skywalker, theres a massive battle and the Final Order fleet is destroyed. Good great. What about the FIRST Order fleet? From what we know that is still fully intact. Ok the senior leadership of the First Order no longer exist (Snoke, Kylo Ren, Hux and Pryde), but the lower command levels are still there. So either the resistance still has a full fleet it needs to face with little or no equipment, OR it now has a couple or more smaller fleets as the First order spilts into different factions. Either way they are in an even worse position than the Rebellion was at the end of Return of the Jedi.
It was never explicitly stated, but I think the First Order fleet was folded into the Final Order fleet. However, since it's much more interesting to speculate on a First Order remnant than to just say, "pretty sure they're stuck in orbit around Exegol and are about five months of food shortage away from cannibalizing each other," here's my musing on a potential FO remnant compared to the Legends Imperial remnant (since the NuCanon remnant was intentionally set up by its own creators to lose it's not as good a comparison point).
Honestly, so much (in fact, almost all) depends on if Rae Sloane is still alive, imo. The reason that the Legends Imperial remnant(s) were so effective (or I should say *some* of them were effective) is that most of the Empire's really talented elites were still alive. They lost Palps and Vader at Endor and Tarkin at Yavin but, aside from that, their best people were still there. Issard was still around, Thrawn was still around, Zsinj was still around, Pellaeon was still around, Ardus Kaine was still around, and for some reason we were meant to believe that Daala was a competent threat too. Whereas, frankly, Rae Sloane is probably the only competent leader that the First Order has ever had. Now if she's still alive then the Resistance is majorly screwed, but if she's dead then the FO remnant is majorly screwed.
However, one *huge* advantage the Legends remnant had that an FO remnant wouldn't was established institutions. The Empire had been the government of the galaxy for over two decades when it fell, its supporters staffed the interstellar institutions that kept the lights on, the holonet running, and commerce flowing. Thus even people who hated the Empire might have still sided with one of the Remnant factions out of fear of greatly reduced quality of life. The FO on the other hand, had only started taking over recently, and didn't even really take full control until between TLJ and RoS. So, in terms of infrastructural investment, the FO was much more like Exar Kun's empire, i.e. just a wandering military force that intimidated obedience out of local governments without really managing them at all. And, of course, Exar Kun's empire had no remnant other than a handful of Sith who would later join Revan.
Given the scenes we get of First Order (not Final Order) Star Destroyers falling down on all of the side planets you remember from the OT (because there was no planets worth remembering in this one) I'd say we're meant to believe the peasant uprising took down the First Order forces all around the galaxy as well.
Ok so what we seem to be saying, is that there is likely a small but functioning First Order remnant out there, which would be in problems unless Rae Sloane was still alive. There is also no functioning Republic, because they were all killed. The resistance has no one left who can step up and help set up a new system. So the end result of 9 movies is that "a Galaxy a long time ago and far far away" collapsed into total Anarchy?
I don't think a potential new New Republic's chief problem would be re-establishing a central government. That would be pretty easy, every world wanting to restore the Republic elects a representative, the reps then meet on Coruscant and form an interim government. I think their real problem would be re-building a national military. The Resistance was created as a guerrilla warfare formation, not a standing military, so they couldn't just seamlessly take on that role. That's why Rae Sloane matters so much, if the FO remnant is led by someone smart who also has a universally respected reputation among the Order, then the FO could conceivably strike while the republican forces are underdeveloped. But if the FO remnants aren't unified and/or waste their time on dumb ideas then the Republic will be able to pull itself back together.