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@Trannamontanna , the mouseholes in the City Living EP  Apartments are tied to the Lot Traits , but unlike in houses, they can not be removed. 😥 This is probably due to us not being able to edit apartments fully... we can change the color of the wall paper, but we can't change the windows, etc.
Apartments with these types of lot traits are viewed as challenges and are part of the challenge of living in that particular apartment!  This does lend to a sense of realism in those apartments, but it does take away from the customization as well. 

The particular Lot Trait in this case is Needs TLC, as seen in the top left corner of the 2nd picture:

There is also a second type of mouse hole that came with the Cats & Dogs EP.  This mousehole can be purchased in Build & Buy Mode and can also be deleted:

As to why it was changed, I'm not sure. I didn't think you could ever get rid of that feature since it was tied to the particular apartment, much how the apartments that have the Historical Landmark Lot Trait won't let you remove the historical landmark plaque that hangs on the walls.  It might have changed when some of the Lot Traits became Lot Challenges with the arrival of Lot Challenges a year ago when Cottage Living was released, but for the City Living Lot Traits, those are not in the category of Lot Challenges, so I don't see why that would affect that.  
Even though the City Living apartment Lot Traits work as a challenge, they are different since they are directly tied to that particular apartment. 

If you are playing on PC or Mac, and don't have a problem using Mods, there might be a Mod out there that allows you to get rid of the City Living mouseholes and roaches, etc. Just know that Mods and CC require maintenance or they can become outdated and mess with your game. 🤨   

If I find out more as to why it was changed, I will let you know. 😉