It’s a matter of the constancy of light and the relative motion of everything else including the non-constancy of time.
Relativity is based on the Lorenz transformation which helps to mathematically bridge the concepts of classical physics and the discoveries in optics and electrodynamics. In theory according to the formula, one could exceed the speed of light, but things would get a bit complex.
At least, that’s my understanding. It’s fascinating stuff.
I think one could create an isolated space time gun barrel like tube through which objects could go through from one end to the other faster than in our universe of “stringed jelly” through which light travels much like a vibration does through a plucked guitar string (where added energy does not increase speed but intensity or pitch). The object would have to be a pure particle and time would disappear.