Resolved! STM32U5 documentation error in HSI -> TIM5 interconnect section
In section 16.3.7 of STM32U5 RM0456 Rev 2, the following text appears in the bullet that notes MSIK, HSI and LSI are linked to TIM2/TIM3/TIM4/TIM5:"External clock mode1: Table 446: Interconnect to the tim_ti1 input multiplexer for TIM5, tim_ti1_in1 (...