If your loading screen loops in The Sims 4 when you launch a game, open a home or load the city map, chances are the game has crashed and will remain in this state indefinitely. This problem can have several symptoms, all more or less linked to corrupted user files.
The first question to ask yourself when you encounter a Sims 4 infinite loading screen, do you have any mods ? If so, remove them and test whether the game works without them. If so, try putting them back a little at a time, and test each time whether the game still works, until you've identified the culprit(s). Once found, these mods will probably need to be updated, but this can only be done by checking the site where you downloaded them to see if a new version is available, compatible with the latest game update.
Each time you remove your mods, remember to clear game cache by deleting the locaclthumbcache.package file located in Documents/Electronic Arts/The Sims 4. This will remove any remaining traces of mods.
If you don't have any mods or CCs, or are still experiencing the problem, a slightly more radical solution, reset game. This won't delete your saves - the game simply won't find them on your PC temporarily. To do this, rename the The Sims 4 folder mentioned above to "The Sims 4.old", for example, then launch the game and test whether the problem is present in a new game. If this works, you can copy and paste the Saves folder inside The Sims 4.old into the new The Sims 4 folder that has been created to retrieve your saves.
