TypeScript Module `gulpfile.mts` Not Supported

I want to use TypeScript with a .mjs (module) Gulpfile. So I renamed my gulpfile to gulpfile.mts, but it says No gulpfile found. TypeScript says it supports the .mts extension here. The above applies to gulpfile.esm.ts and gulpfile.babel.mts and gulpfile.babel.mjs too.