Opening Projects in native tabs Big Sur

Hello,

the last days I opened my projects in fullscreen on the new apple big sur update and my projects were on one window divided by tabs.

But today everytime I open a project the projects opens in a new fullscreen window. Is there a way to allways open projects in tabs? I knew in VS Code there is a option to use MacOs Native Tabs. Is such a option in IntelliJ also available?