Is there a TL;DR for the entirety of Forgotten Realms lore?
For many fictional settings that would be somewhere between an impossible task and the beginning of a meme (like 5 second movies, Honest trailers, etc).
Really, we could play "setting X in less than 3 sentences". For Tolkien's world, I'd say this :
everything was better before.
Anyway, for the Forgotten Realms, there is an answer that is both light/fun and serious :
kitchen sink fantasy.
If you want more information, go spend hours on forgottenrealms.fandom.com. Or watch Jorphdan on YouTube.