To activate the feature, one must first take a rather unusual route and open the dock's setting. To do this, click on the Apple logo on the top left of your Mac and select "System Preferences" from the menu. Then select the item "Dock". Here you will see a drop-down menu next to "Prefer tabs when opening documents". The selection box offers you three options: "Always", "Full Screen Only" and "Never".
Of course, the option "Always" brings you to the desired destination, so that new documents are always displayed in a new tab and do not open in a new window. However, we would like to point out that this only applies to apps that also use Apple's interface for the feature. Some apps have developed their own way to enable tabs. These remain unaffected by the setting.
This restriction also applies to the option "Only in full screen mode" and only opens another tab for a new document if the app is currently in full screen mode. If, on the other hand, you do not want a new tab to be automatically opened for a new document, for example because you prefer to use windows, then you should select "Never" in the dock settings. Once you have chosen one of the three options, you can leave settings again.