Hey there,
On Windows, you probably need to move the butler program to standard location (for me, I created the folder C:\Program Files\butler\ and moved the program to that folder), and then place that folder in your PATH (instructions here: https://www.architectryan.com/2018/03/17/add-to-the-path-on-windows-10/ and these instructions should work for both Windows 10 and 11).
After doing this, restart the command prompt, and butler should be a recognized command.