I’m glad I helped a bit. I’m not sure I know of any videos that cover this. Definitely search for some on YouTube, I’ve never been the kind of learner to seek them out, so unfortunately I haven’t gotten one already.
Now that I think about it, there’s actually perhaps a much better way of doing this since this problem seems specific to just your game/inventory screens. Instead of bothering with a scene manager, maybe it would be better to just make a new Node, called GameManager.
Inside of GameManager, put your current Game scene, enabled, and your inventory, disabled.
Then to swtich, enable one, and disable the other. the disabled ones aren’t processed, so there’s no need to worry about slowing down.
For reference, this is what covers manual scene changing using attach/detach child: