The engine log contains the information what causes the issue.:

[Warning: HarmonyX] AccessTools.DeclaredMethod: Could not find method for type Chat and name OnNewChatMessage and parameters (UnityEngine.GameObject, long, UnityEngine.Vector3, Talker+Type, string, string)
[Warning: HarmonyX] AccessTools.DeclaredMethod: Could not find method for type Chat and name OnNewChatMessage and parameters (UnityEngine.GameObject, long, UnityEngine.Vector3, Talker+Type, string, string)
[Error : Unity Log] ArgumentException: Undefined target method for patch method static bool ValheimPlus.GameClasses.Chat_AddInworldText_Patch::Prefix(Chat& __instance, UnityEngine.GameObject go, long senderID, UnityEngine.Vector3 pos, Talker+Type type, string user, string text)
Stack trace:

HarmonyX fails to patch the Chat::AddInworldText() method. It looks like the function's signature has been changed in Valheim code, so the patch fails and this breaks the mod.

There's also already a bug report in the repository:
https://github.com/valheimPlus/ValheimPlus/issues/709