Hi Tihiy! Thanks for looking into this!
This time I decided to dig a little deeper.
I applied "Win10 Ribbon UI" Explorer style and deleted
HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\Bags\AllFolders
Of course the File Explorer window reverted to its default size and position. I moved, resized, opened, closed and Shift+closed the window several times. It didn't save its new size and position.
I looked into the registry and noticed that
HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\Bags\AllFolders
was not recreated.
Then I applied "Win11 Command Bar" Explorer style and moved and resized the File Explorer window. It saved its new size and position without any problems.
I looked into the registry again and noticed that
HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\Bags\AllFolders
was successfully recreated along with the Shell subkey and all values.
I'm not sure what to think about this. Is it a question of specific permissions? I've installed StartAllBack in "C:\Program Files\StartAllBack" and I'm running Windows as an admin (if that matters).