from what I have learned MPE is for instruments like Roli. MPE control multiple parameters like pitch bend, vibrato, timbre etc of every single note separately when using MPE-compatible software. MPE allows each note to have its own MIDI channel so that those parameters can operate independently per note. Normally pitch bend etc are applied to all notes on a single channel.
I don’t think you need to turn it off unless you have such a controller that supports MPE. I have a friend with a Roli, he can set MPE mode, it was under the device setup in Studio Setup. I only have a Nektar controller connected and I have no options for those settings he had.