As anyone who has stepped barefoot on a stray Lego can attest, the first inclination is to slam dunk the offender into the trash. Followed by any of its kin.
Every Lego set comes with extra parts, which, in addition to the main set itself, can quickly add up to hundreds of parts in any one house. Beyond the larger rectangular building block-style bricks, it seems nearly impossible to do something that feels productive with the remainder of the pieces; they're often not suitable for Goodwill and who wants these things anyway?
You've got some options.
You actually can sell. Someone really does want those things. You can sell whole sets apart or together (especially if you have the box and instructions) and bags of extra pieces. Try Facebook Marketplace for Lego sellers and buyers.
You can return parts to Lego itself. Visit the Lego website to get a prepaid return address label, box up your bricks, and ship. Lego Replay works with Give Back Box, a logistics company that helps reuse discarded shipping materials. Give Back Box sorts and cleans the pieces, then helps send them to nonprofits and charitable organizations.
A handful of other groups do similar work: Brick Recycler; The Giving Brick; and BrickDreams (less active). You can also sell them on BrickLink.
As for whether they're recyclable, Legos are made of a type of plastic that's hard to recycle, so they wind up in landfills instead. The company has said it intends to make the classic toy from a sustainable material by 2030.
