Most people seem to think of 'Protestant' as "[anything] not Catholic"; however, that is not the historical reality.
Protestant denominations are those that "came out of" Catholicism. They "protested" Catholicism - from within Catholicism - and, "broke away from" the Catholic Church - taking "bits and pieces" of Catholicism with them into their newly-formed denomination. (Or, they came out of one of the Protestant denominations that came directly out of Catholicism.)
Not all denominations came out of Catholicism.
There is one [modern denomination] that existed from the time of Christ - well before Catholicism was "a 'twinkle' in Constantine's eye" - albeit, not by the same name.
The Church that Christ built was scattered in the first century - but, maintained the Faith. They became known by different names at different times - and, were later persecuted in the most horrible ways by the Catholic Church. Yet, they maintained the Faith - some even to the death - while being tortured by the Catholic Church.
They eventually became known as 'Anabaptists' - which means "re-baptizers" - named by the Catholic Church - because they did not believe in baptizing infants.
Many of these faithful believers were tortured to death because they would not give into the demands of the Catholic Church that they baptize infants.
They kept the Faith unto death.
The 'Ana' was eventually dropped...
A true Baptist (historically, and even today) is not a Protestant - because, they practice a Faith that did not come out of Catholicism.
If you are interested in knowing more about the history of Baptists, read The Trail of Blood By James Milton Carroll.