@emma_mcdonnell7e I've moved your post to the Sims 4 PC tech section.
First of all, your content is owned by your Origin account, not your computer. So even if you did uninstall, you wouldn't have to pay to reinstall your packs.
For the error, sign into Origin, then try manually launching Sims 4 as an admin, as in, right-click on the TS4_x64.exe (or a shortcut on your desktop, if you have it) and select "Run as administrator." If you don't have a shortcut, you'll find the .exe along this file path:
Program files (x86)\Origin Games\The Sims 4\Game\Bin
If that doesn't help, try either disabling Windows 10's Controlled Folder Access or setting exceptions for TS4_x64.exe, TS4.exe, and Origin.exe.
https://crinrict.com/blog/2019/03/windows-10-defender-controlled-folder-access.html
