I saw it coming from an official port that began as Doom 64 EX, surely their intention was to retain the spirit of the original, and for that adding something like jumping or the ability to look up and down is something that didn't belong to the original. But let's be clear, that features was part of the Kex Engine.
It makes sense for older games like Blood, in which mouselook exists because the Build Engine supported it in the original game and thus was improved in the Fresh Supply port. Doom 64 on the other hand, didn't have that feature as well as jumping, and neither does the other Doom games before it. The GZDoom source port may have added it as a feature, but those willing and wanting a more authentic experience prefer having those limitations instead.
It was expected this could happen. I prefer to play the games the way they were meant to be played. And Doom 64 is one of those cases.
On the bright side, having an official port is better that looking for the rom of the N64 original.