I highly, HIGHLY reccomend going for the "A Card in the Hand" achievement. You have to do basically every single piece of non-High End content other than Ocean Fishing, PvP, Treasure Maps, and Class/Role Quests for it.
The things you can do...
Eureka (all 4 of it, plus Baldesion Arsenal for the ORB) -
BUY A KIRIN'S OSODE OR VERMILLION CLOAK BEFORE GOING IN, IT MAKES IT LIKE THREE TIMES EASIER
Bozja (And Zadnor, and Delubrum Reginae, and DRS for the CERB)
Variant Dungeons (all 3 of them)
Deep Dungeons (all 3 of them)
A Zodiac Relic, perhaps?
Anima Relic, it's a tome dump with some story attached to it
The Warring Triad's storyline
The "Four Lords" storyline
The Sorrow of Werlyt
Island Sanctuary (spreadsheet simulator when you've set it up)
Tataru's Gread Endeavors (Small sidequests that you can do after doing the Shadow of Mhach, Four Lords, and Sorrow of Werlyt quests, there's another 2 after you do all three of those)
Hildibrand, Further Hildibrand, Even Further Hildibrand, and Somehow Further Hildibrand Adventures. The quests are an acquired taste, to say the least. But they're mandatory for the Endwalker Relics, and have two triple triad cards and a mount.
Do the stupid "Allied Society" daily quests. They take a while but they're a quick thing to do every day and you get a funny mount at the end of each one like a giant dandelion. Also most of them are mandatory for A Card in the Hand so...
You can also get all of the EX Trial mounts. There's a special yellow quest you can do after doing this, per expansion.
The best one of them is the Landerwaffe imo.
View attachment 6480495
Giant mechanical dragon that seats 2 players and its BGM is epic. Unlike the EW one that I had to change with Pocket Orchestrion.