Using shortcuts to change font size is a pain because there is so much variation among apps Pages, Evernote, Scrivener etc), even more recently since some apps have adopted Cmd-+/- to change the zoom instead of font size.
Is it conceivable to create a macro to increase / decrease font size across all (most) apps ?
I've also solved this as @Tom with a shortcut. However, more elegantly implemented with BetterTouch Tool. I make this macro ...
I adjust this for each app (cmd +. Cmd - etc.). Then I set the same touchgeste in the different app's. Here is a short video.
At my age one can not remember so much ... already not so many shortcuts
Please excuse my English ... Google Translate is my best friend
Now that I think abou it, I was unconsciously hoping that the solution would include a way to change font size when there is no shortcut available (eg: MS OneNote for Mac)