Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f0/STM32F0x2/USART1/BRR#0x0
Baud rate register
fraction of USARTDIV
mantissa of USARTDIV
https://github.com/modm-io/cmsis-svd-stm32