Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32wb/STM32WB55_CM0P/TIM17/TISEL#0x0
input selection register
selects TI1[0] to TI1[15] input
https://github.com/modm-io/cmsis-svd-stm32