Hi, good day!
I'd first recommend temporarily removing the work or school account by going to Settings > Accounts > Access work or school, selecting the account, and choosing Disconnect. Restart your computer afterward and try switching out of S Mode again.
If the Microsoft Store still doesn't let you switch out of S Mode, try repairing or resetting the Microsoft Store:
Go to Settings > Apps > Apps & features (or Installed apps).
Select Microsoft Store > Advanced options.
Click Repair first. If that doesn't help, click Reset.
Restart your computer and try switching out of S Mode again.
I look forward to your update and am willing to collaborate with you until we resolve the issue. Keep me posted by clicking "Add comments" below.