You must store Game Feature plugins in the Plugins/GameFeatures/ directory. Unreal automatically searches for YourPlugin.uasset in Plugins/GameFeatures/YourPlugin/Content/YourPlugin.uasset.
It is likely (unverified) that your plugin must also have the setting "CanContainContent": true in your .uplugin.
It seems like the tutorial you’re following is probably more trouble than it’s worth, with very basic things not working at all.
I’m assuming that you don’t have much work done in this project so far, which is why my advice to you is this: Throw away this tutorial and the work you’ve done trying to follow it.
Start a NEW project. Do not try to use these broken assets.
Go step by step and test along the way. When you have a good foundation that actually works, then you can try adding your own stuff to it.
Any work you’ve done here you can copy into a functional GameFeature plugin once you’ve gotten one created.
Good luck. 