If you setup different profiles and “switch between the profiles on the fly”, when you close / exit eM Client and reopen eM Client, the user profile that appears “always opens the top profile username in the Profile list” in Settings, and not the one you had opened last.
Yes you can set eM Client to ask on startup which Profile username you want, but if you don’t want to do that and “just open the last profile you had open” there is no way currently to do that.
If eM Client is already supposed to remember the last profile username you had open, it doesn’t work on Mac OS26 or Windows 11 with the latest V10.3.x via the releaser history page.
So if its not a bug, then needs an option in Settings “Profiles” to Set Default profile or alternatively program eM Client to remember the last profile that was open when you close it.