Additional data points here. In March I booked an August stay through the app for what I assumed (correctly as it turns out) was a qualifying rate. It was the lowest available rate (other than bus member, though I didn't check AAA). I called the direct "luxury services" line (800-241-3333) which I've been told is the ONLY way to apply the club upgrade certs. They told me it was a "good" rate, but that there were no upgrades still available (the hotel was largely booked on my dates). I called the hotel and they were able to open up availability for me and tagged my res, and then I called the luxury services line back and they applied the cert. Last month I booked another August stay at the same hotel, but forgot about the upgrade. So yesterday I called luxury services and they said my rate qualified and was still available, and there was upgrade availability. I was a bit surprised as the hotel is quite booked (I got a "resort view" room since the "lake view" rooms are completely booked). Had I booked the same room without the cert it would have been and extra $800/night! Last year IIRC the club premium was closer to $5-600. In pre-covid years it was normally $300. (FWIW, contrary to previous comments, they applied the certs to my existing reservations in both cases.) Also got the $100 credit in both cases, and always have (I've had this card ~9 years).

I've only ever looked at NA resort properties, but I find that if there's a club level room available to book that's identical to the non-club room, the cert will typically work (on the prevailing non-promo rate). And identical doesn't mean i.e. "2 queens"; it has to be the same otherwise (i.e. "resort view" or whatever).