ou probably tried to import a new input system package for multiple input devices compatibility.

These type of errors are due to conflict between old and new input system packages and are

probably resolved in latest updates. To resolve this issue, Go to Edit -> Project Settings->

Player->Under Other Settings under Configuration is the option Active Input Handling.

Select Both. Unity will restart. Now your problem should be solved. You will be able to use old input system packages and the new ones also simultaneously.

Cheers. P.S