So I did a lot more research and found out the “get gameplay tag container” interface only works in C++.
So new strategy, make my own interface which returns the gameplay tags. The “Switch on Gameplay Tag Container” is very wonky. I have no idea how it works. The selection is presumably for a gameplay tag container with a higher hierarchy, and the cases being the tags under it. However, to get the switch to work in my case, I must enter the same tag in both selection and case. which means the switch does nothing…