Hi @AirWhistle68555 - Try selling the desk & chair, then placing a new one in a different location. Make sure the sim can sit on the chair without using the computer. You can also try a different computer.
If that doesn't work, I suggest you try to repair your game -
- Exit TS4 and Origin completely.
- Delete the file localthumbcache.package Default location is C:\[YourUserName]\Documents\Electronic Arts\The Sims 4
- Instructions with pictures are here: https://sims4.crinrict.com/eng/2014/09/delete-cache-files/
- Launch Origin "As Administrator" (Right-click Origin.exe, choose Compatibility tab, Check the box next to "Run this program as administrator")
- In Origin, right-click The Sims 4 icon and choose "Repair". Origin has to be online for this to complete. Let the repair run until completed, on the game and any addons installed
- Launch The Sims 4 and check to see if the issue is fixed.
If you find there's an issue with a particular computer or desk & chair combo, please let us know the details. Happy Simming!