I believe the order of upgrades (like most airlines) is a matrix of status + fare class. i.e. a Platinum with an Econo Flex fare will get upgraded before a Plat with an Econo, and a Plat will get upgraded before a Gold.
Also ... the T&C specify that complimentary upgrades are only available for the member (not people travelling with them) and only on single-person reservations. If you're on a 2 (or more) person reservation, no free upgrade ... even if both people have status. (In my experience, though, they've deviated from that on rare occasion this summer ... probably a 'during covid' deviation from the rule.)