Where to begin?

I am kind of a returning player... joined in 2015 and have been playing off and on for the past two years or so, the majority of that time being off. As a result, I have no idea where to begin anymore. I own PoP, but haven't done much with the expansions since completing Thalumbra.

Is there a master list of what is relevant in the game now (what adorns are current, how the heck to use infusers, etc. )? I am just stabbing blindly into the darkness here, hoping someone can give me direction. It seems there is a steep learning curve these days.

Well you're currently limited to PoP. So start there! Travel to Plane of Magic via the Wizard portal, there is a chest next to the npc that starts the signature line with gear for you to put on to help you get started.
Then read up on PoP timeline https://eq2.fandom.com/wiki/Planes_of_Prophecy_Timeline
There are more in-depth threads located in the EQ2 forums here: https://forums.daybreakgames.com/eq2/index.php?forums/tips-tricks-faqs-and-new-player-discussion.15/

Well, I haven't done anything past Thalumbra. Do I need to work through KA first?

Unless you want your 2.0 the hard way, with grinding factions. I would say no as the experience gained from questing in KA is very poor since PoP opened.
If you had current expac (better yet is to pre-order upcoming expansion as it will unlock all current) once you hit 110, you could do the do the chaos decending timeline and are awarded your 2.0 spells.
If you're an avid crafter, you may want to at least do the KA crafting timeline.

However if you are still wanting to run the KA adventure line, I still suggest you travel up to Plane of magic and get your free crate of gear, it will make KA easier.

Thank you, Kuulei. Doing the KA timeline doesn't give much status?? That is kind of a bummer.

Thank you for the help!