I agree with @tesc and @geo_ . I think things were bad at the end of last year because of Christmas, but especially the strikes. And everything got MUCH worse after January’s cyber incident. BUT, things have really started to improve this last week, especially with mail to Russia and Belarus, which had been at a standstill in February.
I hope everything improves for you too.
Re the postcard to France - this should have arrived. Check that they have logged on recently and that they are regularly registering postcards. If they are, you might want to consider sending them a second card. But you don’t have to. You’ve already done your bit by sending the first. It depends how important it is to you to not have too many expired postcards.
Regarding lots of postcards being sent to you, this thread helps explain it: