There was this thread recently where UI Toolkit was rendering slow on a particular older device: UIToolkit rendering is extremely slow on (older?) Android devices
Reason being a lot of work is put on the shader, potentially causing issues for a mobile device. Once we get shader support I imagine there can be mobile specific shaders.
I haven’t seen any hard figures though the devs have mentioned they test on a variety of devices, and that whether it performs better or worse than uGUI will be different depending on what you’re doing. I’ve seen lots of anecdotal mention of great and bad performance from users, so, hard to come to a conclusion on what people are saying.
On my own anecdotal account, I recently acquired a Steam Deck, and testing my UI heavy, UI Toolkit project on it didn’t have any issues. Not quite a typical mobile device, but not quite a PC, of course.
Needless to say, worth doing your own profiling if you can.