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.
Minimize all applications, press Windows+ m and right-click the desktop.
Select Properties, and select the Appearance tab. Screenshot // Changing the font size of the Sheet name in Microsoft Excel