This is intended for USB/USBCPD applications where the USB side runs at different voltage than the rest of processor/interfaces.
Note, that in the both 32-pin packages the difference is more dramatic than just presence of VDDIO2 (and related absence of PC6/7) - this is in line with the same "GP"/"N" variant in 'G07x https://community.st.com/t5/stm32-mcu-products/difference-between-quot-gp-version-quot-vs-quot-pd-version-quot/td-p/183326
Note, that nature of VDDIO2 "ring" (IO supply domain) in 'G0 is not the same as VDDIO2/VDDUSB in some other STM32, as there is no isolation switch.
Also, RM0444 says, " Although VDDIO2 isindependent of VDD or VDDA , it must not be applied without valid VDD"; however, I can find no mention of this constraint in the 'G0B1 datasheet... ( @Imen.D , can this detail please be clarified? Thanks.)
JW