I am having this error as well. I haven't played the game in a while but all my maps are now broken and never load. as well as getting this error popup on startup.

I've been getting this message as well/ I have been away for five months. I've made changes to my MODS and it will not go away.

Last played 12/11 - no problems
As of 12/13 - with the update designed for latest DSL release, Financial Districts, I too am now experiencing this error... Is it my punishment for not bowing to the 'pay it to use it' gawds of Paradox for not buying this latest DSL? Or will play be on hold for another month like how P/P broke users' games did?

I got the same error due to the latest DSL release.

I too am getting the same error message.

Mine fixed simply after unsubscribe then subscribe this mod

From @algernon
"Getting in before the inevitable rush, and in the (probably vain) hope that people will actually READ THIS BEFORE COMMENTING:

An error with the word 'Harmony' in it following the latest update will NOT be because of this mod. Such errors will most likely be due to not having the latest 1.16-compatible updated versions of:

- Loading Screen Mod Revisited
- 81 Tiles 2
- Repaint

All of these mods have been updated to work with the latest game versions, but earlier versions will cause Harmony patching errors when run against the updated game version. As always, if this happens:
- Unusb/resub the mods to try to get them to update
- If that doesn't work, restart your Steam client and/or computer"

Details:
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> HarmonyLib.HarmonyException: Patching exception in method null ---> System.ArgumentException: Undefined target method for patch method static System.Void EightyOne2.Patches.ElectricRoadPatches::GetColor(UnityEngine.Color

having this error,anyone can help?
unsub/sub mod also restart PC didn't work

also can't save the game and this error appears when saving

Array index is out of range. [System.IndexOutOfRangeException]

Details:
No details

On native Linux, it crashes with every single mod using Harmony. On the Windows version, it works fine with the exact same set of mods. It used to work on Linux some month ago. Some update must have broken it. Everything else still works on my Linux system and the game runs fine with mods not depending on Harmony.

Originally posted by generaljaker:

From @algernon
"Getting in before the inevitable rush, and in the (probably vain) hope that people will actually READ THIS BEFORE COMMENTING:

An error with the word 'Harmony' in it following the latest update will NOT be because of this mod. Such errors will most likely be due to not having the latest 1.16-compatible updated versions of:

- Loading Screen Mod Revisited
- 81 Tiles 2
- Repaint

All of these mods have been updated to work with the latest game versions, but earlier versions will cause Harmony patching errors when run against the updated game version. As always, if this happens:
- Unusb/resub the mods to try to get them to update
- If that doesn't work, restart your Steam client and/or computer"

Re-subscribing and restarting the computer did nothing, i'm done with those issues