I do love LibreOffice, but who thought this colouring is a good idea? https://i.imgur.com/cUzW97S.png

If anyone else wants to be rid of it (courtesy of astra): Set NotebookbarColorTransparency to 255. This removes the colored tint while keeping the ribbon.

Go to Extras → Optionen → LibreOffice → Erweitert → Experteneinstellungen. Search for NotebookbarColorTransparency. Double-click the matching row under org.openoffice.Office.Common → Misc. Change 150 to 255. Confirm with OK, close the settings, and restart LibreOffice.