Is Baptism needed for salvation?
Can infants be baptized?
Is Jesus truly present in the Eucharistic bread (the Lutheran consubstantiation) or not?
And of course I can add the gulf between Evangelicals and the Liberal historical Mainline Protestants as well as the Arminianism vs. Calvinist debate.
Liberal, historic mainline Protestant denominations have all but completely abandoned Scripture.
They can hardly be considered churches any more when they don’t teach the truth found in Scripture.
As far as those examples, they are no more major than the ones that exist between the EO and RCC.