Where an LMS is administration-first (assign, track, certify), an LXP is learner-first (discover, explore, get recommendations). LXPs curate content from many sources and use personalization to surface what each learner should see next.
In practice the line is blurry — most platforms now include elements of both. The right question is usually whether your priority is compliance and tracking (LMS strengths) or engagement and self-directed learning (LXP strengths).