From this situation, we know that he is very unsatisfied with Spurs management. It makes sense if he played badly and showed bad performance during this season. He doesn't want to play with Spurs anymore, he must have very low motivation in playing. I think it is natural and acceptable although in the other hand it seems a bit unprofessional attitude.

I think so. Man City must let him go, there is no advantage to keeping him on the squad. Spurs management is better to focus on looking for another top striker to replace Kane's position.