You 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 ...
New does not guarantee heap allocation and simply avoiding new does not guarantee stack allocation. New is always used to allocate dynamic memory, which then has to be freed. By doing the first option, that memory will be automagically freed when scope is lost.