No, the Lexar CFexpress Type B Professional Gold 128GB is not compatible with the OM System OM-5.
OM System OM-5 has an SD-only card slot (no CFexpress support of any type). Its own spec page confirms only SD/SDHC/SDXC card compatibility — CFexpress Type B uses a physically different connector and cannot be inserted into an SD slot.
What works instead
See all compatible memory card for the Lexar CFexpress Type B Professional Gold 128GB →“SD Memory Card (SDHC, SDXC, UHS-I, UHS-II compatible)”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)