help: how to fix the hole in my new mesh ?

You will need to disable backface culling in blender, press the "n" key to open up the sidebar and under shading disable the "blackface culling" checkbox





You will also need to enable double faces inside sims 4 studio


to enable them import your mesh and enter the warehouse and select a geometry and go to the data tab, (you will have to do it for each geometry) under materials --> items, click on edit items











Now click on add, select the newly added entry, where it says field change it to "double sided" and then change the value to 1











Now just save everything and it should work, it won't show correctly inside sims 4 studio but it should work fine in-game