This new patch fixes the multiplayer bug and several others across all platforms.
UPDATE 3/23: Today, FromSoftware and Bandai Namco released patch 1.03.2 for Elden Ring, which offers several bug fixes including one that stops players on PC getting hacked by an invader. The patch is available for PC, PS4, PS5, Xbox One, and Xbox Serie X| S, and is required if you want to continue playing in an online state. The other bug fixes include one that stopped players from advancing NPC Nepheli Loux’s questline, another that caused death when trying to descend from a spot near Bestial Sanctum, and another that prevented Ash of War, Endure from taking effect. The patch should be offered next time you load the game on consoles and applied automatically if playing through Steam.