I'll start by saying I don't think this is an intended feature, but forgive me if it is.

So I'll start by saying that I am level 120 at the moment in power and also add that prior to going to asgard I was around 80-ish. Prior to going to Asgard, the basic enemies and some Mystery Event characters were all labelled as green in difficulty due to having significantly lower power levels within Grantebridgescire and Ledestescire or however you spell the two power 20 areas.I had finished both areas' alliance chains prior to going to Asgard and enemies within the areas retained their levels. After exitting asgard, enemies in both areas are no longer green, and as such I can no longer one-shot headshot them with the hunting bow, nor can I assassinate even the weakest of them in one hit (I went warrior first, so I was expecting this for higher level areas, but not for areas that are supposed to be labelled as green.) Additionally, East Anglia is labelled as green after leaving Asgard and enemies within it are scaled to my level as well (white). I have not done the alliance quest chain for East Anglia yet, nor have I even started it.

I reloaded some saves to test things.
One before Asgard- All enemies that should be green are green and have their level set to the area level.
One during Asgard but not finished with the quest chain related to In Dreams- All enemies are set to being my level unless they are a higher level by default.
One after Asgard quest chain is finished- Same as the second result.

This is rather jarring if it remains like this for the rest of the game as part of the power creep of the game is dealing more damage and having higher health to deal with enemies, but if they scale to your level you can throw all that out. No point in having good damage or defense values when even the beginning area enemies (Yes, I tested Norway as well) hit you just as hard as the later area enemies.

It's also worth pointing out that Mystery Event enemies are not effected by this. For instance, I fought the Walloper after Asgard and he was green. The old Drengr of Ragnar Lothbrok north-east of Fornburg was also labelled as green when I fought him after Asgard while every other non-event or generic roamer enemy is white. This is mainly what led me to believe this is a bug. I was under the impression enemy level scaling was removed to make the game more interesting and engaging than the ridiculous scaling style of Odyssey.

If this is intentional, so be it, but I don't understand why it would be intentional. It essentially invalidates overleveling as a strategy to guarantee assassin or bow skills or even warrior combat skills work well enough to be used without as much heavy investment. I thought that was more or less the point. This is not a complaint about game balance either, I'm having fun and not running into many issues, but this seemed like a pretty glaring issue.

Alright I did some further testing to be sure and the point at which Enemy Power level is stuck on the player's power level is actually right after the dane attack on the settlement after finishing the first 2 power 20 areas' alliance quest arcs (The attackers I figured were supposed to scale to your level but I don't think it's supposed to make everything else scale to your level as well.). I'm going to progress for now and see if it self corrects after doing another scripted event at some point during or after other alliance quests. The target dummies outside of Hytham's bureau are good indicators since some of the dummies there should almost always be green and others have been red in the past but now they are all white or red.

After leveling up some more, the enemies are green again (In L.scire, G.scrie, E. Anglia, Ox.scire, and Southern Norway. Player Power Level 130), but seem to be retaining the stats boost they got when Raventhorpe was attacked.