Some people do poop in the shower.
Around 1 in 30 people have pooped in the shower on purpose and some people have accidentally pooped in the shower.
More people however pee in the shower than they do poop in the shower.
Peeing in the shower is not as bad as pooping in the shower as peeing in the shower is easier to clean as the pee is simply washed down the drain while you're taking a shower.
Pooping in the shower would require you to physically clean up the poop as the poop would not easily go down the shower drain.
It's better to poop in the toilet and not in the shower.
But if you need to pee while showering you can simply pee in your shower and the water from the shower will wash the pee down the shower drain.
I pee in the shower all the time but never have pooped in the shower.
I did once however poop in the bathtub as a kid and was having bowel issues but that was an accident and not on purpose.