If you're going to play a Winter Eladrin in 5e, the best recommendation I can make to offer about that specific culture of Eladrin is the original article on Winterkin Eladrin. Now, the lore will not be a perfect match, because 5th edition has actually quite heavily reworked the basic assumption of who the eladrin are, even whilst staying true to 4e's basic concept of them as "the Feywild Elves", but it is the original point from which 5e's "seasonal shifting" eladrin were derived, so it can't hurt to check it out.
Winterkin Eladrin are detailed in "Winning Races: Winterkin Eladrin", by Robert J. Schwalb, in Dragon #384, released in February 2010.
As for Eladrin as a whole, if you're playing 5e, you don't really need to look at their lore past 4th edition, because the original Eladrin were very different. Introduced in AD&D 2nd edition as part of the Planescape campaign setting, old-school eladrin were Celestials (Outer Planar beings native to the Upper Planes) who embodied the alignment of Chaotic Good. They all looked like elves (save the two subraces who looked like pixies and aquatic elves respectively), could transform into an energy form, and were officially Not Related to the elves despite their appearances.
4th edition eladrin, which are the root of 5e eladrin, basically took the names of the eladrin, mixed it up with the High/Gray Elf subraces of AD&D, and rolled them into the Feywild. 4e Eladrin are the "Magic" Elf Race (compared to regular elves, which are the "Primal" Elf Race). They are city-builders, focused on arcane magic and civilization's benefits over nature, and the single most powerful and organized race in the Feywild, essentially taking the place of humans in their traditional "dominant race" slot in that plane. Good sources for 4e eladrin are Wizards Presents: Races & Classes, the Player's Handbook 1, and Heroes of the Fallen Lands.
For information on the Feywild, you want to stick to the original 4e lore, as that's where it was invented; the closest thing to the Feywild in the original Great Wheel is the Archfey's Court, a demiplane that travels across the Chaotic Upper Planes, and the optional Plane of Faerie from 3rd edition, which is... minimalistic. I do not recommend reading any of the homebrewed Feywild supplements offered on the DM's Guild, because in my experience they largely ignore everything 4e did and just offer their own reinterpretation of 3e's Plane of Faerie. The best sources on the Feywild in general are the 4th Edition Manual of the Planes and Heroes of the Feywild. There are also a number of articles in the 4e run of Dragon & Dungeon magazines that touch upon specific Feywild locations.
For the Archfey in particular, again, stick to the 4e lore - the original Great Wheel Archfey are literally just names and a table listing worshippers, symbol and associated planes in the back of the Planescape splatbook On Hallowed Ground. 4e Archfey Lore, in addition to the Feywild books I mentioned above, is found as a series of articles in Dragon & Dungeon Magazine called "Court of Stars"; these are the fully-detailed Archfey of 4th edition, and the Archfey article on 1d4chan mentions others that didn't appear in the Court of Stars, including several specifically associated with the Forgotten Realms:
- The Prince of Frost (Dragon #374)
- The Carrion King (Dragon #420)
- Thrumbolg, First Lord of Mag Tureah (Dragon #420)
- Hyrsam, Prince of Satyrs (Dragon #422)
- Cerunnos, the Horned Lord (Dragon #428)
- Selephra, the Bramble Queen (Dungeon #185)
- Baba Yaga, Mother Of All Witches (Dungeon #196)
- Tuxil, the Trinket Lord (Dungeon #205)
