Berkeley's Idealism

[Neo-Scholastic]

The very validity of proof or evidence relies on existence independent of any perception.

Agree. The question is whether perception occurs in physical reality or a purely mental one.

If existence were determined by perception, then there would be no such things as facts - since facts are required to be independent of any perception - and without facts, there would be no such thing as a proof.

One need only provide a mechanism in which to ground facts. That ground could either be an enduring physical reality or a universally enduring observer. Both share the quality of Being-in-Itself.