Are the D4 add-ons like the mainstory (or in previous Diablos) or do they play out in freeroam?

I haven't played much beyond the campaign because i couldn't replay it like in previous games, so i stopped playing. I have seen that some story-add-ons came out since release in 2023. Are those campaign like the main story or will i play in the "freeroam" world (no clue what that's called)