Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/STMicroelectronics/STM32U031/SYSCFG/SYSCFG_ITLINE27#0x0
SYSCFG interrupt line 27 status register
USART1 interrupt request pending, combined with EXTI line 25
https://github.com/cmsis-svd/cmsis-svd-data