As far as I've collected, just attacks (like unarmed or weapon) can be used with Extra Attack, but when I add Shocking Gasp spell in my dndbeyond character sheet, it has checked by default the Display As Attack checkbox inside the Customize section for the spell. I have seen the same effect with spells like Chill Touch or Vampiric Touch.... is there a special rule that allows those cantrips to be used as attacks? or this is just a bad-default-data scenario?

Thanks in advance

It is due to the spell requiring an attack roll to hit an opponent and does not need a saving throw so it is a spell attack.

On the character sheet, “Attacks” doesn’t mean “actions that use the Attack action,” it just means “actions that require an attack roll.”