Can You Play Solo on Xbox Live? Yes—But Internet Required

Yes. "Playing by yourself" on Xbox Live means:

• Single-Player Games: Any campaign/offline mode works while signed in (achievements unlock, cloud saves sync).
• Solo vs. AI: Many multiplayer titles offer Solo / Private Match vs. Bots (Halo Firefight, Gears Horde solo, CoD Combat Training).
• Async Multiplayer: Forza Drivatars, Dark Souls messages/bloodstains, Death Stranding structures — you interact with ghost data, not live players.
• "Looking for Group" (LFG) Off: Simply don't join a party; appear Offline (Profile → Appear offline) to avoid invites.

Hard Requirement

Internet connection — Xbox Live authentication, license checks, cloud saves, and system updates all need periodic online access (at least once per 30 days for "Home Xbox" offline licenses).

No internet = no Xbox Live features (but disc games still launch in offline mode on your Home Xbox).