(I’m using time-sensitive words, even though we are stepping out of the spacetime of our universe for parts of this discussion.)

Maybe use different words, so as not to imply that there is a temporal, causal, or spacial relation.

Many people realize that, conceptually “below” or “before” any “base universe,” there is

I don't realize or accept that.  Anything that would be in those categories are inaccessible to our universe, and not knowable or reachable from within.  They are literally imaginary.