Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32c0/STM32C011/SYSCFG/SYSCFG_ITLINE27#0x0
SYSCFG interrupt line 27 status register
USART1 interrupt request pending, combined with EXTI line 25
https://github.com/modm-io/cmsis-svd-stm32