I was thinking about removing the resonator from my exhaust but I watched a video saying that it will negatively impact the car as naturally aspirated cars need back pressure as it helps get rid of the gasses faster, is that true?
Also do mufflers provide back pressure and do sporty mufflers provide less?
With all else equal, removing the resonator or muffler will reduce the restrictions in the exhaust pipe. This means that the ability of the exhaust headers to flow gases will increase, not decrease.
However, this does not necessarily mean that the engine will produce more power, since that is the result of several subsystems working together. So if the exhaust is bottlenecking performance, reducing exhaust restriction will improve performance until the point that something else becomes the weakest link. If something else (like air intake) is already the weakest link, a better-flowing exhaust system will have little impact on power.
Vehicles that employ wideband lambda sensors are sensitive to backpressure; they can tolerate deviations up to a point, but beyond that the engine may run too rich or too lean.
While zaid's answer is correct for the OP's 4 stroke engine, the exhaust design for a 2 stroke engine can be more complicated. Rather than benefitting from a free flowing exhaust, exhausts for 2 strokes are often tuned to create wave fronts that suck exhaust fumes from the cylinder and at the same time stop unburnt fuel being sucked out.
Small 2 stroke motorcycles exhausts are good examples of these, where there is a large expansion area, but then a very small exhaust port at the end. While the design may appear to be very restrictive, they are in fact tuned to make the engine more efficient.
See the Wikipedia page - https://en.m.wikipedia.org/wiki/Expansion_chamber
