“ if the universe truly consists entirely of mathematics there has to be an observer“
Who says so?
In mathematics, your statement of
“I had a pie and I didn't cut it into 8 slices”
would look like this:
When you didn’t do anything to the pie, you removed it from the mathematical operation. It is no longer a dividend of a division problem, or an operand of any mathematical operation. It’s just a fucking pie. (edited)