Never play pvp and you will keep your sanity If you choose to ignore this advice Bungie has mental health channels you can utilize.

It is daunting as there is a lot to do. If you want to build out your character so it has access to all the abilities across solar, arc, void, stasis, strand and prismatic then you will be best served working through the main dlc campaigns from oldest to newest which will spawn various quests to unlock stuff, by that time you should have a fair amount of weapons and armor that will help you tackle the harder activities like dungeons and raids.

Make sure you have prismatic then the dungeon with the best loot is vespers host

Personally, I'd just play the campaigns in their respective order and their corresponding side quests as you go. There are 20+ seasons of story and narrative that are no longer accessible so the campaigns, dungeons, and raids are it. Dungeons are tough so unless you are a skilled player, I'd advise a +1. Raids are 6 man, but can be done with less people if skilled enough. Expansions are as follows: Shadowkeep Beyond Light Witch Queen Lightfall Final Shape A book could be written on the intricacies of D2 so, imo, this is where I'd start. Also, work on you Guardian Rank objectives up to, I think 5, which will allow you to use mods on your armor.

If you’re doing dungeons, I’d recommend starting with Shattered Throne (the dungeon in the Dreaming City) or Pit of Heresy (on the moon), as those are definitely the easiest ones for a newer player. Definitely don’t try Vesper’s Host or Sundered Doctrine until you’re more comfortable with the game.