UID12786 Did you move the Sims 4 user folder to the desktop in an effort to fix the crashing issue? If so, that's where your saves are. You can move them back to Documents > Electronic Arts > The Sims 4 > saves now. The same goes for other files you'd like to keep, although your mods and custom content may not be working at the moment. So test those files first if you want to keep them.
If that's not the reason your data disappeared, please see this guide to finding missing user files:
⚙️[PC] Sims 4 Missing User Content (saves, mods, etc.) | EA Forums - 12636780