The same cell modes are still available, they’re just labeled differently.
Rather than calling them “JavaScript” and “TypeScript”, they are now both called “JavaScript”, and there’s a separate “Strip types” option, enabled by default, to run TypeScript natively. (You should almost never need to disable Strip types; it’s there mostly for backwards compatibility to avoid opting all existing JavaScript cells into type stripping.)
JavaScript with Strip types off is equivalent to the old JavaScript mode, and is labeled js.
JavaScript with Strip types on is equivalent to the old TypeScript mode, and is labeled ts, and is the default for new cells and when you pick JavaScript from the cell menu.
I changed this to address a different confusion where people don’t know that TypeScript is a superset of JavaScript, and seeing TypeScript was confusing, causing people to look for a JavaScript cell mode even though they could have used TypeScript. That confusion was raised here and here.