Hi,
in kde I would like to start an instance of an application like the kitty terminal with no title / menu bar and no borders. How can it be done?
Thanks

You can use the special window settings. Easiest way is to rightclick on the titlebar of a running instance and select "More Actions" → "Configure Special Application Settings". In the following window select "Add Property" and add "No border and frame" setting.

In Systemsettings this is found in Appearance → Window Management → Window Rules.