Yes, I mean the engage button.
By default, no matter the trim, the engage vs button is going to put you in a -500 fpm. (Readed in the display) , then you can rotate the knob and change but it will you put you in -500. No mather the last fpm settings. It’s the same to alt engage button. When you set a desired altitude and press engage alt it will put you in a +500 by default.
Regarding yo vs engage button, to get a 0 fpm by pressing it you need to first be matching the real alt and the display alt