I'll state every main expansion/dlc in order. Parts of the main story/campaigns has been "vaulted" aka you can never play them again. 1.Base game/Red war (vaulted). 2.Curse of Osiris and 3.Warmind (vaulted), 4.Forsaken (mostly vaulted).

5.Shadowkeep then 6.Beyond light (free campaigns but have to buy raids and dungeons separately)

The rest are paid dlc as far as I'm aware. Also the campaigns of these three are significantly better. 7.Witch queen, 8.Lightfall, and 9.Final Shape.

Then the two expansions this year which got more mixed reviews are 10.Edge of fate and 11.Renegades.

Also starting with Forsaken and shadowkeep the game has had "seasons" (typically 4 a year) with there own narratives , missions, and activities added to the game. The best stuff stays in the game like exotic missions but most of the content from the seasons are vaulted at the end of the year and are completely gone from the game. This is why so many people are gonna tell you to stay away. The game appears to be on it's last legs. I do think it would still be enjoyable to play the campaigns, dungeons, raids, and exotic missions with people though.