For one example, "pi" is an integral (ha ha) part of Gauss's Law, and of Ampere's Law, which partly describe electromagnetism. Designing the computer you're typing on, and the communications systems that form the internet by which you pose your question and I answer it, depend on a proper understanding of that field (ha ha). Pi is also involved in the Schroedinger equation, fundamental to quantum mechanics. Design of solid-state devices, among many other things, is at least partly dependent upon understanding that field.
So, aside from the area and circumference of circles, and the volume and surface area of spheres ... pi may be hidden from your view, but it is fundamental to the modern world you may well take for granted.
And, by the way, eiπ + 1 = 0
That’s my favorite pi equation - Euler’s Identity!
Euler as one the other mathematicians of his era said “The master of us all!”.