I've pulled a handful of these apart, some easily, another not yet. That flat spring is to provide tension between the two sections to reduce slop.
The rubber boot can be pulled back to expose more of that area. Then flip the shaft over and look for a line imprinted in the grease of the upper shaft. I have one like that that I haven't figured out how to get apart. There has to be a nub or such that hits a stop. As it stops solid, metal on metal.
On one I was able to find a pressed in nub and carefully drilled it out. Note that these shafts are from various vehicles that use the same one.
Others have pulled apart with no issues.
RemoveBeforeFlight