Downloads from gallery not working

@sydneyc111  You absolutely do not need to install Windows 11, and frankly there's a good argument to be made against doing so, since it could complicate the troubleshooting process further.  If it did end up helping, that would likely be because your current OS is corrupted in some way, but you can address that with a repair install of Windows 10 insteaad.  It's not at that point yet though; creating a new user account is easier and less drastic and takes less time.

Let me know how it goes.

I opened it in another Windows account and it worked! Is there any way for me to make it work on my account? Or am I just doomed to always have to use another account haha

@sydneyc111  This strongly suggests that some user setting is the problem, whether it's one you set deliberately or something like restricted permissions imposed by an antivirus.  We could go through the possibilities on your normal account if you wanted; the place to start is with the Documents directory.  Here's how to reset permissions:

https://winaero.com/reset-ntfs-permissions-windows-10/

In this case, the full path of the Documents folder is this:

C:\Users\[your username]\Documents

and you'd want to reset permissions for its subfolders as well.

There are other ways to troubleshoot too, so if this doesn't work, you still have options.  But at some point, it may be easier to switch to the new user account.  You can move your data there, whether only your Sims 4 content or everything else too; there's no harm in having multiple accounts or in switching to a new one.

It says "Access denied" :/ Any idea how to fix that?

@sydneyc111  That's a bit unusual, but one possibility is that OneDrive is running and blocking access for... reasons.  You can pause or cancel a sync easily enough:

https://support.microsoft.com/en-us/office/how-to-pause-and-resume-sync-in-onedrive-2152bfa4-a2a5-4d3a-ace8-92912fb4421e

If that doesn't help, or you don't use OneDrive, you should be able to use the takeown command to give yourself full permissions:

• Restart your computer, and don't open any applications
• Hit Windows key-X and choose either "PowerShell (Administrator)" or "Command Prompt (Administrator)," whichever option is offered
• In the window, write this command:  takeown /F "[full file path]"  with the quotes.  In this case, you'd write "C:\Users\[your username]\Documents" except with your actual username inserted.
• Double-check the command (take note of the two spaces in the command line), and when you're satisfied, hit Enter
• Restart your computer again

If you get an error message, please post a screenshot.