Before Inventor 2010, add-ins are loaded into Inventor by running registry mechanism in a command prompt. It was complex procedure. So, the registry free add-in mechanism was introduced into Inventor 2010.
Now in Inventor 2022, the registry based add-ins will not be listed in the Inventor Add-Ins Manager dialog as default. So, it is recommended to convert registry based add-ins into registry free add-ins. The guidelines to convert registered add-ins into registry free add-ins is explained in the below article.
https://help.autodesk.com/view/INVNTOR/2021/ENU/?guid=GUID-CFFA5CC6-38E6-4ACD-A2BC-8B8732727996
In case, registered add-ins are can't convert. The registered add-ins in current version can be enabled by modifying below registry key.
HKEY_CURRENT_USER\Software\Autodesk\Inventor\RegistryVersion26.0\System\Preferences
LoadRegisterBasedAddins = dword:00000001