Im not sure if this is a bug or not but, it tracks the coordinates of an entity in the nether with the same coordinates in the overworld.

Other than saying it is being currently loaded or it is alive there is no way to know if it is in the nether or not.

Here's what I would say: have the compass say the person is in the nether and point to the nether portal they went into

Secondly with the tracker command, when in the overworld give the 8x coordinates and the coordinates to the portal and in the nether have everything behave normally.

I'm not a mod creator or anything so I don't know how difficult this all would be

The compass is not capable of tracking entities across dimensions.
Although, I will consider this as an enchantment or something.

alright, thank you!! my friend and I are trying to have a compass that can track both of us individually as the command block tutorials only really allow for a one person set worldspawn sorta deal, i got the command blocks to be able to give one the compass with the designated nbt tag to track a specific entity, the final hurdle is just the dimension thing which is way out of my league in terms of coding and stuff.

anyways, thank you for responding and considering this as a potential addition! :D