The Sheet tabs in a workbook are part of the Scroll Bar.
Change the font size in the Scroll Bar option to change the font size of the Sheet name in the tab.
The default settings for the window view in Excel are determined by the Windows operating system and Excel.
The applications/code on this site are distributed as is and without warranties or liability. In no event shall the owner of the copyrights, or the authors of the applications/code be liable for any loss of profit, any problems or any damage resulting from the use or evaluation of the applications/code.