From what I can see, the error suggests that a previous version installed is causing the problem.
Please keep in mind I’m not related to the butler project, please be careful trying anything I suggest.
Try uninstalling butler, and then take a look at the folder in the error message (C:/Users/<username>/AppData/Roaming/itch/broth/butler) and see if that’s still there. If it is, then maybe try deleting it before installing butler again? Keep in mind if you do that, you will lose data related to butler on your machine.
As far as I’m aware, the AppData folder is used to store local data related to a program. If that program is uninstalled, the folder in AppData of that program should be able to be removed without issues.