Checked your lodestone profile, you might want to at least Zenith your relic weapons first. Myths are easy to get now so you can replace your gears with the full Valor/Hero set at least. All new dungeons can be unlocked via quests given in 7heaven at Mor dhona (except Lost City, taken from entrance to conjurer's guild). Once you get plenty of Soldiery tomes you can exchange them with the Weathered Noct chest, which is a good upgrade. You can proceed with the main scenario quests Leviathan and Ramuh primal fights. Gilgamesh fight can be unlocked through Hildibrand sidequest

Lost City/Brayflox HM/Halatali HM is the dungeon set from 2.2, brayflox is quicker and lost city is slightly difficult for newcomers.
They continued the Crystal Tower story by adding a new 24-man instance, Syrcus Tower. You can get ilvl100 items here.
Tamtara/Stone Vigil/Hullbreaker Isles is the latest addition, theyre difficult if unprepared so you might want to gear up first.