How to open folders (e.g. by click from desktop) in a new window instead of a new tab?

You can go under File Associations and set your favorite application for folder, when choosing Dolphin, you can go in Application properties and add the command line parameter --new-window before the %u

On Kubuntu 22, Open start menu, find Dolphin, right click and choose “Edit Application”. Then on the Application tab

Source: kubuntu – KDE – Dolphin: Open folder in new window instead of new tab – Ask Ubuntu