certain quests (like solo raids) offer very high amounts of xp. Normal content and boosts barely raise xp after lvl 60 so you need to look for xp “coins” that you can trade in at the store
Daliy quest also offers a good amount
If you didn't complete some Story Quests then you could go back and do those.
I am Valiant endgame and I never explored Act 6 or 7, after a while rewards just weren't worth doing that content anymore. But now I am going back and exploring them because you get 1.5k-3k XP per fight with boosts.
In reality, you need to be Valiant to be able to level up beyond 60. You need access to refined XP which is 1k times the value of regular XP, but only Valiants can get it. If you're not Valiant, you won't be leveling up anytime soon.
Tks for the replies.