It certainly exists/works, but is it productive? With my time using Tamagui I would go with no.
There are just so many traps everywhere. 99% of it isn't your fault, just the name of the fragile RN game. Install another package here to handle one use case on one platform, avoid this component on one platform because RN doesn't support this thing, entire blocks of very simple styles commented out due to performance cost. List goes on. It's a never-ending game of your codebase feeling horribly fragile, and that's if you remain within the RN = Android and iOS realm. As soon as you start trying to get it to be truly cross platform with desktop apps - endless nightmares.
I so desperately want cross-platform development to feel as smooth as people proclaim, but it's really like playing russian roulette with every new component added. At the end, you question if it was really worth it due to how much you've had to rewrite anyways. You become sort of delirious after working on a project that uses such solutions, wondering if you traded user experience for developer experience and wound up messing both up in the long run.
Beautiful site/docs though.