Post-religion directly correlates with less friends, less peers, less in-built community, etc.

You can have all those things without. Many do. But it requires extra work that organized religion does for you, and we're talking about a problem where people aren't having kids because they are extra work

Surprisingly (for secularists), post religion means degrowth of the culture.

So it’s a good thing if you want Europe’s culture replaced by what the data show is happening, and it’s a bad thing if you think Europe’s traditional culture is worth saving.

Well where I am (Edinburgh) we have a superabundance of culture at this time of year - very little of which has anything to do with religion?

I’m alluding to the long term trends(one - two generations out, assuming they follow the behavior of the last two generations).