Hi
@Sylvie8701 welcome to the forum
There are some apartments with balconies already so that might help. You can't actually build your own apartments in The Sims 4 so if you bulldoze a lot you would still be left with an apartment building in place it is just that your sims apartment would now be empty. If you try to move the outside walls to make a balcony in an apartment that doesn't already have one nothing happens as it is outside the buildable area.
So, if you want a balcony, as far as I can tell you have to move into an apartment that already has one. You can look at all the apartments in the Manage Worlds menu by clicking on the apartment block, then the specific apartment you want to look at, then the build option becomes available.
I also moved your post as it was in the wrong place.