Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32h5/STM32H523/TIM3/TIM3_AF1#0x0
ETRSEL=B_0x0
TIM3 alternate function register 1
etr_in source selection
0 (B_0x0): tim_etr0: TIMx_ETR input
1 (B_0x1): tim_etr1
15 (B_0xF): tim_etr15
https://github.com/modm-io/cmsis-svd-stm32