Missed Approach Procedure, get the FMS past the runway or MAPoint. If you hit NAV, it will just follow the lateral NAV source selected—LOC unless you manually toggle to FMS. Only with GA button will it automatically change source from LOC to FMS. I just remembered, there is an FMS track to the MAP, as you intercept final from FMS. If you selected FMS source, then NAV, you get guidance right thru the procedure w/o cycling the FMS manually. I retired off the Global earlier this year, things are already fading.
There’s three ways to do most everything in Collins, so different ideas prevail.
GF