ALT codes are used to enter special characters and symbols on your PC. These are combinations of the ALT key and numeric keys. A specific ALT ad numeric key combination is used to enter a specific special character. But, some users cannot use ALT codes on their computers. This issue might be caused due to your configured settings or a certain app interfering with your keyboard shortcuts. It might also be caused due to a Registry entry preventing you from using ALT codes.

Here are a few fixes and suggestions:

1] Switch on Mouse Keys while Num Lock is enabled.

2] Modify the Registry to activate all Unicode characters.

3] Uninstall the problematic app.

4] Switch to another Keyboard Layout.

5] Use Character Map to enter ALT codes.

6] Troubleshoot in a clean boot state.

Learn more on https://www.thewindowsclub.com/fix-alt-codes-not-working-in-windows-11-10