A toolbar is simply a menu - a series of commands - packed into a rectangle. Typically it extends horizontally across the top of an application.
A toolbar can be simple, like the one in Notepad ...
... or it can be complicated, like the one in Word 365 ...
(Technically, the toolbar is the part at the top: File, Home, Insert, Draw, etc. The bottom part is what Microsoft calls a ribbon. People hated it at first.)
The taskbar is a menu that extends across the bottom of your monitor when you use Windows ...
The main difference between a toolbar and the taskbar (some people capitalize the 'T') is that a toolbar has commands whereas the Taskbar has shortcuts to apps.
Unless an app offers a command to enlarge its toolbar font, there's no supported method to make the font (only) larger. And you shouldn't look for an unsupported method to do this, because (1) it's never a good idea to make unsupported changes to software - which is why I won't advise it - and (2) app developers build the app's user interface on the basis of the fonts they choose. If you try to change the font, the interface will look weird, at best, and you can break the app, at worst.
If you're having a hard time reading toolbars - welcome to the club - try Settings > Accessibility > Text size or Settings > Accessibility > Magnifier.