I’m in the same boat; I’ve had the AW Series 7 for only one week now.
The Belkin Boost Charge Pro Portable (which I bought from the Apple Store) worked great for the first two days, until I updated watchOS to 8.5.
Fast-charging was a major factor in my choosing Series 7 over the SE; my use requirement for the Apple Watch is pretty much 24/7, so I needed to be able to do quick charge-ups a couple of times a day. For the first two days using the watch, I could do this easily. Since watchOS 8.5, not so much.
I’m sure that disabling fast-charge (on at least some chargers) in the OS update was done in error, but from what I’ve found online, it’s at least the third time that Apple have done this (8.1.1, 8.3, and now 8.5, apparently).
I can understand making a mistake, but to keep making the same mistake repeatedly really shakes user confidence.
The fast-charging design Belkin have deployed in these chargers is surely made to Apple’s specification, so I am really struggling to understand how this problem has arisen in the first place, let alone several times now.
Apple, could we please get some sort of commitment to stop breaking fast-charging with future OS updates? That would really mean a lot to many of us Apple Watch S7 owners, I am quite sure.