Core Problem:
When building a nether portal above the default world height limit in a world with an extended build limit via datapack, such as at y=700 for example:

and trying to teleport there from a portal in the nether:

the portal leads to a "strange place":

The "Strange Place":
It is impossible to move. Looking around shows the overworld dimension effects and all mob/player entities that would be present at the same coordinates in the nether. For example, it is possible to watch players move near the portal in the nether. Relogging places you back in the portal in the nether as if you had never gone through it in the first place.