Oh - i have to correct myself: i now tried out again pushing the comma by holding it and moving the finger - and surprisingly the diacritics appear while
letting the finger pushed! Maybe it is because a few days ago i installed the multi keyboard layout beneath the one you mentioned ? But i didn’t recognized any change in the behaviour of the keyboard, so i deinstalled multi keyboard layout again.
But now mystically they shown up! I am a little bit confused but it’s ok. With this kind of behaviour i can live
Btw.: the gif isn’t animated within the phone’s Forum- application but in (desktop-)browser it works!