So mtg arena is going to work on mac this winter, but i am so disappointed to learn that it only has standard format . Does people still play the old mtg online game where we can play many formats as commander / modern ? Does it still exist ?

yes they do you can check prices for cards at different sites but I would recommend mtgotraders as they are on the marked for long long time and you have seasons now so you can play 5 matches when you have time to play them and you have normal challenges where you need to be there for whole duration