Looking for online courses for mobile design

Hello everybody!
Can anyone suggest me some online platform where I can follow courses to design the UI for a mobile applications?

I just recently realized that in order to develop a good looking app I should first throw down a design that convinces me and then apply it instead of continuing to make small adjustments that I'm never satisfied with.

If anyone has any general advice about the ui/ux on mobile applications, any suggestions are appreciated!

Thanks a lot!