Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32c0/STM32C011/SYSCFG/SYSCFG_ITLINE21#0x0
SYSCFG interrupt line 21 status register
Timer 16 interrupt request pending
https://github.com/modm-io/cmsis-svd-stm32