this is of course a narrative to suit an argument without substance.
a 'normal' family (as far as one can define normal) has give and take, it has love and support and respect in both directions - it has nothing to do with dictating.
And yes, adults will reminisce about their children / grandchildren / nephews and nieces / god-children and even children of close friends - remembering the fun moments, the embarrassing moments, the celebratory moments - all of that is absolutely normal, to suggest otherwise is to build a narrative of a dysfunctional society that actually bears no resemblance to reality
but then this is an argument coming from the same stable as men being able to become women and v.v. so perhaps not surprising that reality is not involved.
children once they have grown up - accept it as a part of the banter of family life - they might groan and say, 'mum do you have to' but it is accepted as a part of their shared history and with recognition that they all belong to something that can not be removed - membership of that family...
an adult child telling their parents not just that they can not reminisce, but that they must fake the history and pretend a fabricated set of lies has already walked out of that family unit - they have blown it apart in an attempt to re-manufacture reality to a shape they desire...
So, unsurprisingly, you have it back to front - the parents have every right to share what was real, what happened, and what was a large part of their shared years as family...
a grown up child does not have unilateral right to dictate, and especially not to fabricate alternative realities and build a fragile web of lies and expect everyone else to bow down and worship at their imaginary past and future.