USUALLY the problems people experiences with fastboot is related to the communication with the watch.
Either cable, port or driver.
Silly as it may sound on Windows11, a 'newer' USB3 port might cause problems. On my Lenovo X1 Yoga gen 6 (20XY), I can not get fastboot to work directly. But if I use an old usb2 hub, things works fine. It also works fine if I go via my thunderbolt 4 docking, and a USB3 port on that.
AFAIK, there are fewer issues if the machine is on LINUX.
You might also try from an old PC with USB2 ports only.
Usually it is not super picky on the cable, but try sw