Was the Forge Version for Lithium removed from Curse and why? Will it be back soon? I can't upload my pack on curse using the Forge Version of this mod, it gets rejected.

Lithium has been split into separate curseforge pages for fabric and forge. You can find the forge one here: https://www.curseforge.com/minecraft/mc-mods/lithium-forge

Hm. It's not possible to find that page via search:

And also not via Twitch App.

ah, because you have no release version
Thats why Curse rejects my upload containing the alpha file.

I've changed the Forge releases to use the Beta type.