In Linux I use PageControl1.ActivePage.Font.Style := [fsBold]; or PageControl1.Pages[1].Font.Style := [fsBold]; to change the font style of an individual TTabSheet title. In Windows 10 neither works, I can change every TTabSheet title font style in the PageControl by using PageControl1.Font.Style := [fsBold]; so it's not that Windows can't display a bold font style.
Is this some kind of weird limitation of Windows ??