Is it safe to continue using Big Sur on my macpro

Apple has continued the convention of providing security updates for the currently-shipping version and the two previous versions.

At this writing, that would be the current 12 Monterey, and the previous 11 Big Sur and 10.15 Catalina.

From what I read on the Internet, Apple will still provide security updates for Big Sur for at least two years or longer.

There is no Mac Pro 2014 model, perhaps you're confusing it with a MacBook Pro.

A Mac Pro is a desktop computer. A MacBook Pro is a laptop.