Armrest, under the seat, in the trunk (where the styrofoam cutout is for retractable trunk cover).Just got an 2018 Outback last week. My old car, a VW, had a nice cubby in the glove compartment where to store the manual. Is there a place in the Outback where the manual is suppose to live, aside from taking over the glove compartment?
If you haven't done so already, register on mysubaru.com. Once you have, log into your account and you will find Support & Resources link at the top, and there you will find complete manuals (not the individual sections).
I downloaded my pdf file from https://carmanuals2.com/subaru/outback-2017-owner-s-manual-96964