Even after the upgrade to the generation 2. I think the 12 pro max won’t go far enough into the pocket to reach the charging coils. I think the pocket is to small for the phone.You have to upgrade he charging pad to the next get version. 2017 doesn't charge qi which is what apple uses.
The one that I tried was a Brandmotion from Crutchfield it would not charge my iPhone 12 Pro Max which is slightly smaller than your Samsung S21 Ultra. I sent it back. Maybe the GM Generation 2 will work with my iPhone.I think it is more a matter of placement of the charging coils in the pad. My phone sticks out quite a bit.