never, because it feels insincere even when you or others used unironically and meaning it, years of assholes using it sarcastically and attached to toxicity made me reject it.
In party chat to the team, but I never go out of the way to say it someone who just beat us. As much as I want to give them props I know they will take it the wrong way and bug the fuck out.
I've long been a very sore loser, at least in my own head, so I'm extremely diplomatic when I win because I project that the other party is feeling worse than they probably are.
Almost never. I rarely play multiplayer games, and when i play i rarely use voice chat. I think i sent some GGs in the game chat to my co-opers in monster hunter world some times when defeating some of the endgame monsters. Otherwise i never bother to send a private message just to say GG.
I play on console so it depends on the text chat options. In rocket league where its simple enough I consider it kinda rude not to. Probably a bit daft to think like that but a positive end, win or lose, goes a long way.