https://www.typescriptlang.org/tsconfig/#erasableSyntaxOnly covers them all, I strongly recommend running with that option enabled to be future-proof.

enums and decorators mainly. There are also subtleties such as having the ts file extension in imports. Also imports aren't transpiled in cjs so you need to need es modules.

I'm using it in my projects with no issues.

Your comment might lack explanation, but indeed the TS team has mentioned multiple times that they don't want to add any more features that require transpilation (as opposed to "dumb" type stripping and being a strict superset of JS).

IIRC they "almost" recommend against using them (the last part, I haven't researched again now).

But the usage of many features has reached a sort of point of no return, so I hope Node will go the route of making the experimental transpilation the default for TS files at some point.

Goes to show how strong the appeal of syntax is, especially enums.

To people coming from languages with enum support, it just looks so much more organized to use them, compared to union types, despite all of the (many) drawbacks.