I’m guessing you installed vanilla Rider that doesn’t have the Unreal plugin installed or updated.
Make sure you have the UnrealLink
Rider plugin installed, then install the RiderLink
plugin in your game.
Also check in Languages > C++ > Unreal Engine and make sure you have Enable UnrealHeaderTool inspections
checked. (There are some other great options to check in there as well).
Good luck, hope this helps.