I don’t think there’s any one right answer to this. I can say for me personally, I have stayed away from online smash entirely unless I’m playing in an arena with a friend. The net code is too buggy and the progression of gsp is scaled in a way that can make it really frustrating to see that number drop drastically after a couple of consecutive losses. If you still want to play online I would recommend doing something else while you play (ie. listen to pidcasts, watch tv/a movie, listen to an audiobook, etc.). Especially with smash I think it’s important to allow yourself to laugh at the jank that can happen when playing online. Also, if you are looking for competitive practice, playing online—when losses sometimes feel cheap—can add another level of frustration to the grind of becoming a competitive player.
At the end of the day, it’s important to cut yourself some slack and recognize that you will get mad. The most important part is trying to release that frustration in a healthy and non toxic way.
Hope this helps.