if you're only interested in the lore and not the gameplay itself then i recommend reading stories on https://akgcc.github.io/cc/story.html its a great tool, and using the wiki pages to read character bios. theres also plenty of youtube vidoes of the cutscenes if you wanna read them that way. the gameplay itself does add a bit thematically to whatever story youre reading and may help you immerse more, but it can be a slog if you just want to get to the story. a lot of arknights stuff is really great but do be warned a lot of the most recent stuff is very long, so treat it more like a book than video game lore.

id recommend reading at least the first few chapters of the main story to get a good feel of the initial worldbuilding. other than that, twitter posts and wiki pages can be a great starting off point if you dont know quite yet what interests you, since theres a lot to arknights lore. for example if you like what you hear about laterano you may want to read stories like Guide Ahead and Hortus de Escapismo. good luck!