You can actually. FF14 let’s you run “trusts” which are just dungeons where your party is a bunch of NPC bots drawn from the story’s roster.
The only thing you can’t do it for iirc is the end game raids, but those are generally not connected to the main story very directly.
No problem! It’s actually handy for learning dungeons and stuff cuz you can watch the NPCs who rarely mess up their positioning.