No, the Delkin Devices POWER CFexpress Type B 128GB is not compatible with the GoPro Hero12 Black.
GoPro HERO12 Black has a microSD-only card slot (no CFexpress support of any type). Its own product page confirms only microSD card compatibility -- CFexpress Type B uses a physically different, much larger connector and cannot be inserted into a microSD slot.
What works instead
See all compatible memory card for the Delkin Devices POWER CFexpress Type B 128GB →“Memory Storage microSD 1x microSD™ rated class A2 V30 or higher”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)