It was actually on Forge first and got ported to Fabric. I think it also says that on the Fahric mod's page, that's why I know it.
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I think it was originally on Forge based on my memory where I was disappointed after seeing the trailer and trying to play with it. I couldn't though since I was using Fabric and didn't want to use Forge.
New Mandela effect just dropped.
No, I always remember it being a forge mod, since the 1.15 days at least. Not sure what to tell you. Maybe they discussed Fabric but went with Forge in the early stages? Maybe you're thinking of being frustrated with it not being a Fabric mod and having to install Forge? Maybe you're thinking of another mod entirely?
Others have already answered, but just to confirm as a big Create fan, no it was not originally a Fabric mod. I played with it on Forge since the early versions on 1.14 and I remember eagerly awaiting a Fabric release.