How to change font and font size in Print module under Photo Info

The font sizing is set in terms of points - 1 point being 1/72 inch - so actual print scaling is used based on the page setup. If you are (say) exporting to JPG for someone else to print, you can game this to your advantage.

As an example, if you consider an A4 page layout with a certain point size for the text and a certain output resolution - but change the page layout to A6 instead (half as wide and half as high as A4) while doubling the output resolution to compensate - the same JPG output dimensions can effectively be produced with the same photos shown in a same-looking grid.

But for a given font size as expressed in points, any text will show up proportionately larger within a page layout, when that has smaller scaling. In that A4 > A6 example, text would have doubled its apparent size.

"It also seem impossible to add custom characters into the photo info space, eg "ê.""

There is a similar bug with the Book module -- you can't use the standard Mac method for entering Unicode characters:

https://community.adobe.com/t5/lightroom-classic-bugs/p-can-t-type-unicode-characters-in-book-module-on-windows/idi-p/12662948

Please add a description of your issue with the Print module to that bug report, and be sure to add your upvote in the upper-left corner.

As a workaround, enter the text into the Textedit app and then copy and paste into the Custom Text field in the Print module.