The watchOS 8.5 update appears to be breaking fast charging on the Apple Watch Series 6 and Watch Series 7. Experiences vary, but some third-party chargers have stopped working completely.
https://www.notebookcheck.net/Fast-charging-issue-identified-in-watchOS-8-5-for-the-Apple-Watch-Series-6-and-Watch-Series-7.611058.0.html