Windows missing after applying wallpaper?

@CoolTjej_90 This sounds very frustrating! Thank you for including your screenshots. I would like to begin troubleshooting by doing a repair and removal of cache in a specific manner as outlined below please as out first step:

If you have never in the past had Mods or CC in your game, just skip the part about deleting the Mods folder, but still delete the cache file mentioned. If you ever had Mods or CC in the past then do the Mods folder deletion, as there could be damage that has remained after you removed them - plus the config file from the old Mods folder could have become corrupted.

• Exit your game then exit Origin. Delete the mods folder and the localthumbnailcache.package file in your 'The Sims 4' folder. (When you restart the game will re-create the Mods folder if you deleted it.)
• Then run a game repair [ Open Origin, click 'Game Library' then right-click Sims 4 > Repair Game ]. Make sure to let it run until it has completed all repairs (it will do the base-game first, then run through each of your expansions/packs). After that, please see if the issue has stopped.

Also... can you please upload your lot to the gallery for me to download and test in my game?  You can name it something like 'deleted windows test' and post here the exact name you used plus your EA ID (your user name in the gallery) - or you can just add a link to it here.

Let us know how it goes. Thanks!