As detailed in TCon3 Fabric PR#8, inventory tabs binds to Mantle's ModularScreens just fine, but due to ModularScreen reporting a bogus backgroundWidth/ImageWidth in order to work properly, the spots you need to click to open tabs are offset dramatically, as seen in this video:

As far as we understand, ModularScreen stores the useful width value in a property called realWidth

I'm not sure if there's a solution to this that doesn't involve an unwanted mantle dependency, or a PR to mantle to de-cursify their code. But I think a non-dependency fix here using an alternate method of calculating click hitboxes, or a PR to fabric-mantle, is the way to go.

As mentioned on Quiltcomm I'm happy to dig into this one with you 👍 We mostly wanted to post a proper issue here so less people go and complain on TCon3-fabric's repo that this is broken.