No, the DJI Osmo Pocket 3 is not compatible with the Lexar CFexpress Type B Professional Gold 128GB.
DJI Osmo Pocket 3 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 camera for the DJI Osmo Pocket 3 →“Supported SD Cards microSD (up to 1 TB) Recommended microSD Cards”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)