Has anyone created a class on DND beyond here that is basically the UA Mystic?  I found Tasha's psionics to be quite disappointing. And I do not want to reinvent the wheel if someone has already done the heavy lifting...

Right now it is impossible to create a whole class in D&D Beyond.  All you can do is a subclass off of an existing class.

Is this where you make my dream come true and tell me you have a sub class of the UA Mystic already done and ready to share with me?

There are 4 pages of subclasses in the homebrew section that are either called Mystic or have it in their name.

https://www.dndbeyond.com/homebrew/subclasses?filter-name=mystic&sort=rating

Maybe one of them will be what you're looking for - or close enough that you could base your own homebrew on it.