It seems that based on the video and referenced sources, its "upstream" (libraries) projects turning to alternatives to TypeScript due to the effort in setting

It seems that based on the video and referenced sources, its "upstream" (libraries) projects turning to alternatives to TypeScript due to the effort in setting types and apparently there are easier ways to provide type support for their users ("downstream"). I'm curious if anyone has experience as a "downstream" TypeScript developer and if they have similar issues to these projects mentioned.