Love this thread. Taco is going through his teenage years and seems to have energy to burn at the minute 😩 I'm trying to come up with games for him. I have a puzzle very similar to the one in your picture @JENGOSMonkey and Taco loves it, but the more he plays with it, the better he gets and now only keeps him occupied for a few minues. I haven't tried an empty egg box yet, I like that idea.
I also use a snuffle mat sometimes for kibble and it keeps Taco entertained for 20 mins or so. And any games that involve using his nose really tire him out! So like hiding treats around the house and making him find them. He does it with his toys too.
@zande I was so so nervous at first when they started to play, because they were totally silent, no growling at all. They still are mostly silent apart from their scampering/slamming/sliding/knocking-things-over sounds lol. Not worried at all now and rewarding them for sharing spaces seems to have helped significantly more than the whole "let them figure it out for themselves" idea.