Understand the Calculator in W|A?

Questions
1

so I know the site has a calculator, but I want to find out the point where it overflows. I’ve been getting interested in large numbers but couldn’t figure out the overflow. Can someone tell me what it is?

2

Try 9^9^9^9

3

Try

$MaxNumber
4

Scratching my ego, I tried entering “4976th digit of the MRB constant” and got an answer. However, when I tried “4977th digit of the MRB constant,” I got an empty matrix.

5

I mean the highest number or alternative it will even show, like 10^10^10^10^10^10…
Or extreme functions like Ack(x,y) (the Ackerman function)
Or maybe something completely different
So far what I’ve got is Ack(?(7!),?(7!))