This material is not under the OGL
For material to be under the OGL, it needs to state that it is licensed under the OGL. Neither the Unearthed Arcane pages, nor the document itself have such a statement, so it is not licensed under the OGL.
Instead, the material states that it is copyrighted
©2020 Wizards of the Coast LLC
So unless the material has been later included in the game proper and made been available via, for example, the System Reference Document that is licensed under the OGL, you cannot use it under OGL.
Copyright protects the form of the material, but it does not protect general concepts or ideas. The term psionics itself is not copyrighted, and you could use it, or refer to the material in general terms. However, you would not be able to verbatim include these psionic rules.
Remember, this is not legal advise, I am not a lawyer, nor do I play one on the internet. I play a Hobgoblin.