STM32 gotchas
51.Not all TIM_CHx are created equal

Timers, besides having the counting unit (prescaler and counter) and the control harness, they have several Capture-Compare channels. These don't have the ability to count, yet they represent most of the inputs and outputs of the timer (besides external clock inputs and "emergency" break inputs), which usually also connect to the actual pins (through the GPIO matrix). They also input/generate (through the control harness, or sometimes even directly) the internal signals going from/to other peripherals within the chip.

In STM32 timers, there's a varying amount of channels in various timers (1 to 6, 4 channels being the "gold standard"). The channels also have somewhat varying capabilities in different timers - good example of this are the complementary output and break features of channels in Advanced Timers. Mostly, timers with the same number have similar capabilities and similar number of channels across all STM32 families, but exceptions do exist.

However, even channels within one timer are not equal when it comes to their capabilities. Here is an incomplete list: