Qt allows to place QDockWidget as "tabified" on the left hand side.

The tab can be set as "verticaltabs".

The tabbar height increases with number of docks.

On all styles, if the tabbar excceeds window height, arrows are inserted to easily scroll between the tabs without incresing widget size.
The style "MacOS" does not do that, it increases tabbar size and hence the whole window size without limits thus making the window unusuable.

Changing the style on OSX to anything but MacOS fixes the issue.

The attached minimal example demonstrates the issue (it may be necessary to increase the number of docks to see the effect).
Original issue: https://github.com/texstudio-org/texstudio/issues/3637