The Elder Scrolls V: Skyrim (2011) and Skyrim Special Edition (2016) are single-player games. They have no official online multiplayer.
The Elder Scrolls Online (ESO) — Separate MMO (Buy-to-Play + Optional Sub). Set in same universe, different gameplay.
Verdict: If you want to play Skyrim with friends today: PC + Skyrim Together Reborn. On Xbox/PlayStation: Impossible officially or via mods.