Roll damage if it hits

[Qoff]

Is possible to roll automatically the damage if it hits?

[Trenloe]

Nope. It's always (at least) a two step process. It gives the GM a chance to verify/approve before players roll for damage, sometimes people forget to apply the correct modifiers/effects before rolling. It also would be incredibly complex to do this with multiple attacks/targets. So, it's always been the two step process.

[Brynnan]

Agreed. You have things like casting Shield or Counterspell, etc. Legendary Resistances, Combat Bardic Inspiration. There's a lot of things that could change the outcome between the To Hit roll and the Damage Roll.