Visiting other households

Have you just walked up to their house or did you purposely travel there?

You have to travel to the lot and get the loading screen for the house to load properly, if you don't get a loading screen, you will only be able to see a shell of the house

I tried both ways. I’m living in a apartment at the moment so I clicked on next door to go visit and the loading screen came up and I tried travelling there as well 

If you're using mods please try without them. If that fixes the issue then use the 50/50 method to work out the problematic content and remove/update it

https://twinfinite.net/2020/02/sims-4-broken-mods-how-fix/

Also try repairing your game:

https://www.carls-sims-4-guide.com/help/cache.php

@LucyLocket_x95Hi!  It is normal for the lot you are visiting to collapse to the floor when your camera is really close to the lot.  Apartments are different because the exterior wall doesn't collapse but the door is invisible in Walls Down view.  Try changing to Walls Cutaway View or Walls Up view to see the door.

This shows Walls Down and an invisible door.

This shows Walls Cutaway and a visible door.  Then you should be able to click on the door to get the "knock on door" option. 

When visiting a lot that isn't an apartment, you can also click on the floor of the house to get the "knock" option when the walls disappear.  I've noticed this doesn't work on apartments though.  I only get the "knock" option if I have Walls Cutaway or Walls Up and click on the door.

Thank you I’ll try that way!!