Can't read Flash size data register from uart bootloader with micro STM32L4

[ACaso.1]

Following the "RM0394 Reference manual", I'm trying to read the "Flash size data register" using the Base address: 0x1FFF 75E0 with the USART protocol (serial) but i receive the NACK response.

I see in the Memory Map of the "RM0394 Reference manual" that the address 0x1FFF 75E0 is in a RESERVED space, so i realize can't read the "Flash size" and the "device uid" through the bootloader USART protocol.

Is there some other way to get it?

I'm using a Chip ID: 0x435 wit BootLoader protocol version: 3.1