Hello there, ever since I began developing here, I saw a ton of UI designers, and I thought it was a very interesting career. Sadly, tutorials for this is no where to be found, and I don’t even know what tools do I need/do I need scripting knowledge, etc.
There’s no sure way of learning UI other than doing it yourself! I encourage you to just start making stuff as you’ll learn fastest this way. Don’t be intimidated, you’ll find your mistakes as you go.
However here’s some tips than can help you:
Knowing the difference between Scalar and Pixel when positioning or sizing GUI elements (This one is important)
Knowing how to use UIConstraints (Like UIGridLayout or UICorner)
There are also many tutorials on youtube that you might’ve missed:
As said before, just go for it and you’ll learn along the way. There is no BEST or FASTEST way to learn, but I recommend making some kind of menu GUI or something to start.