Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f1/STM32F101/ETHERNET_MAC/MACA0HR#0x0
Ethernet MAC address 0 high register (ETH_MACA0HR)
MAC address0 high
Always 1
https://github.com/modm-io/cmsis-svd-stm32