Is there a limit to how much knowledge the human mind can acquire? If so, what determines this limit and why does it exist?

No.

There is no limit.

The structure of the gray and white matter is such that the more that you learn, the deeper the surface area becomes in our grooves, sub, grooves, micro, grooves, subatomic, grooves, etc.

See Mandelbrot.

Then you will understand.

No, there is no limit.