My sims have a huge problem with interacting with their apartment neighbors. If my sims visit them, I don't have options to interact, the only solution was to make them temporary selectable and play the neighbor. When my sims ask them to come out, they come out and immediately go back without any option to interact. The moment I make them temporary selectable, my sims can't call the neighbor anymore. I obviously found the solution but it's extremely annoying. I wish my sims could interact normally cause I love playing apartments.

Probably a mod issue. Try taking out your download folder and see if that fixes it.

Personally, I highly doubt this is a mod issue as I've also had this happen frequently, including back when my game had very few mods installed none of which affect apartments, and have seen other people discuss the same bug as well.

I've never once found a way to consistently fix it. For me, what it looks like is: "Stuck" neighbors stay permanently in their apartments and if you go in to interact with them, your sim can interact autonomously but you can't get any options when you click on them. If you make the neighbor selectable their action queue says they are trying to "sleep" on an icon of a book (which I think is the placeholder that the game uses for what the neighbors do to automatically refresh their needs inside their apartments while they're not visible, but they got stuck that way?). You can cancel this action, but as soon as they're made unselectable they immediately go back to trying to do it again.

It doesn't happen to every neighbor always, but once it happens to one of them it sticks around. If you move your sim out of the apartment and back in again (which is a huge pain), it will fix their neighbors but there's no guarantee they won't get stuck again. Neighbors might not be stuck on different sublot copies of the apartment (i.e. if two playable families live in the same apartment, the same townie neighbor could be fine when you play 1 family but stuck for the other one).

The only workaround I've ever found is that this ONLY ever happens to townie neighbors, not playable families. What I've had to do is make some townies playable and move them into the apartments they're supposed to be in, but just not actually play with them (so they're not really part of my playable households, but they'll stay in that apartment unit and function like they should). Maybe that's an OK workaround for you.