The Sims 4 won't load past main menu

@shotofanxiety  As a test, please try playing in a clean user folder.  Move the entire Sims 4 folder out of Documents > Electronic Arts and onto your desktop, and when you launch the game, a clean folder will spawn with no content.  (Your saves and other content will be intact in the folder you moved but temporarily not read by the game.)  Don't add anything to the new folder yet; just let me know whether you can get far enough to start a new save and play in live mode for a bit.

If that works, restart your computer and try again.

If that doesn't make a difference, please let me know what antivirus you use and whether OneDrive is running on this computer.  Please also run a dxdiag and attach it to a post.

https://help.ea.com/en-us/help/pc/how-to-gather-dxdiag-information/

So, I did as you suggested and moved my TS4 folder out of the EA folder entirely.  I made a test sim, and she worked fine, so I moved my mods folder back into the TS4 folder (I had done this before I saw your reply, which is why I added it back into the folder), and slowly applied them to a new sim, testing between each bit of custom content to ensure that it worked.  I think the problem was some hair CC I had by Anto from The Sims Resource, because when I got rid of those, the issue resolved itself.

However, now whenever I try to use the gallery to place a new household and actually have it show up in my game, I face the same endless loading screen.  I am able to recover a save and load it normally, so I don't know if it's the gallery acting up, or something still funky with my game?

@shotofanxiety  Are you saying that merely trying to open the Gallery causes endless loading, or the household or lot you're using is the issue?  Plenty of Gallery items are broken, or at least incompatible post-For Rent.  (Some may have broken later than that too.)  So if you're choosing a household or lot and it's not working, try a different one.