i get asked often how i syncretize judaism and islam (understandably!) but probably my least favorite "question" is when people say "well you can't syncretize that because X and Y beliefs are different." i fear people don't know that syncretism isn't just simultaneous practice of several beliefs but is indeed the forming of new beliefs/traditions from those original ones.
also, if religions A and B had no differing beliefs, they would be the same religion!! thus making syncretism impossible in the minds of some people. i respect the confusion but it gets so tiring to explain this specific thing lol