Congratulating other teams on their success.

Not a very long, complicated or stunning question, but I was just wondering why it isn't possible to congratulate a team if they have one a competition/cup you have participated in?

I'm sure this happens in real life, and the use it could have in FM is that it gives you a better relationship with that club and its manager, making it easier to buy/sell players from/to them. And it could boost/decrease the morale of the squad, as they might think it's professional or not ambitious (depending on the personality of a player) to congratulate a rival.

you can say that the manager has done a good job

I've never understood why players think its unambitious when you praise another manager anyway. I don't see any relevance to ambition whatsoever.

Not a very long, complicated or stunning question, but I was just wondering why it isn't possible to congratulate a team if they have one a competition/cup you have participated in?

I'm sure this happens in real life, and the use it could have in FM is that it gives you a better relationship with that club and its manager, making it easier to buy/sell players from/to them. And it could boost/decrease the morale of the squad, as they might think it's professional or not ambitious (depending on the personality of a player) to congratulate a rival.

Can't you do it on the "Manager Interaction" sub-menu? (Squad screen, same menu with "Assistant Advice", "Clear Selection",etc)

Well no you can't, you can only say a manager is doing a good job, but that's not really what I mean.