OK, the correct location for EditorLayout.ini, where your layout is saved, is:
C:\Users\USERNAME\AppData\Local\UnrealEngine\4.21\Saved\Config\Windows
The correct location for BaseEditorLayout.ini is:
C:\Program Files\Epic Games\UE_4.21\Engine\Config
Replace USERNAME and 4.21 with your relevant values of course.
And overwriting BaseEditorLayout.ini will not work. You have to manually save the ini file and overwrite EditorLayout.ini.
Same with engine prefs. We can save these prefs as ini, in Unreal, but we can’t load them from Unreal. They seem to be in BaseEditorLayout’s location, but I haven’t messed with those yet.
Thanks EPIC for making it a pain to handle your software’s layout. And for constantly changing things around, so it’s even more of a pain to understand your changes.