The gameVersion array for version 1.38 from the API is empty. I assume this is why it is not available for download from CF or the Twitch client. Did you select 8.3.0 when you uploaded the file?

Well, it seems to work now, though gameVersion is still empty 🤷

The reason for the delay was simply that CurseForge has to approve every single package. Usually they are very fast, but this time it took time than usual.
I also do not upload the file myself. Whenever I tag a version in git, GitHub automatically triggers a Webhook which automatically triggers packaging and distribution on CurseForge. I also never set the gameVersion myself, this is done by CurseForge with the current version or maybe they read the version in the toc file.

Something must've gone wrong on their end then I suppose for the gameVersion array to be empty.