Why is the Option Bytes of STM32G474xx chip isn't one-to-one corresponding to its register?

[RLai]

Category 3:

In Option Bytes: (0x1FFF7800)

Bit 22 DBANK:

0: Single bank mode with 128 bits data read width

1: Dual bank mode with 64 bits data

This bit can be written only when PCROP1/2 is disabled.

Bit 21 Reserved, must be kept at reset value.

Bit 20 BFB2: Dual-bank boot

0: Dual-bank boot disable

1: Dual-bank boot enable

But in register : FLASH_OPTR (0x40022020)

Bits: 22:20 Reserved, must be kept cleared