Utils::QtcTabBar, the designed Tab/TabWidget component has varying sizes depending on the currently set QStyle, and therefore the tab component does not follow the specified design in Figma.

Windows:

macOS:

Figma design:

The reason is that Qt's stock QTab and QTabBar use various pixel metrics to define size of tabes in a tab widget. The current implementation of Utils::QtcTabBar just overrides the paintEvent, which does not suffice.
In order to have ultimate control on sizes and spacings, it seems to me that metrics and painting of Utils::QtcTabBar need to be done via custom QStyle implementation.