Do not create union types with Redux Action Types. It's most likely an antipattern.
So, there is a long-standing TypeScript & Redux pattern of creating a union
RootAction type that contains all your application's action types. Sometimes, you would also create a lot of reducer-specific sub-unions.
I think that this has always been a crutch - and given the options we have today, it's most likely an antipattern.
So let's look at why it was used, where it was used and what you can use instead.
Why was it used? A look at typed Reducers.
Classically, these action union types were created to use the Discriminating Union pattern.