Step 6 on the following page is incorrect.
Running Blueprints at Unreal Editor Startup | Unreal Engine 5.1 Documentation
The documentation says “Find the DefaultEditorPerProjectUserSettings.ini file, which is located in your Project folder at Project/Config//DefaultEditorPerProjectUserSettings.ini. Open it in a text editor.”
Instead, it should say
“Find the DefaultEditorPerProjectUserSettings.ini file, which is located in your Project folder at Project/Config/DefaultEditorPerProjectUserSettings.ini. Open it in a text editor.”
Thanks to this post for the fix. 4.23: How to auto-start Editor Utility Widgets? (new feature) - #11 by Veseliy