Sombra is not a backline assassin, unless there is an enemy in the backline with no peel you shouldn’t engage the backline unless it’s to distract the Ana from healing - any good Ana, Zenyata or Lucio will out duel you 1v1, you have no hope vs Moira and you can only out duel a Lucio or Brigitte if you get the Hack off first.
If you’re playing on attack, then you should be waiting for your Winston, Wrecking Ball or D.va to dive and then turn the fight into a 2v1. Otherwise you want to play with your team, shoot barriers and look to intercept something with Hack.
Solo Sombra play is awful and will just get you reported, if you’re going to use Stealth then do it to set up cross fires but not hard engagements - barring EMP plays.