Century Gothic font cant print specific character u+03bc in bold

With your font set to Century Gothic Bold, launch the Emoji & Symbol viewer (ctrl+cmd+space). In that panel's search field, enter 03bc and you will see the Greek small letter mu revealed. From the Font variation selection of these characters, locate Century Gothic Bold and double-click that particular mu character to insert it into Pages. It will be a bold mu character there too.

I recommend that you add this to Favorites so you can just double-click that mu variation in the future.

I can duplicate this Century Gothic Bold μ character issue with Pages v13.2 on macOS Sonoma 14.0, at least when exported to PDF. One workaround is to use the Pages equation editor to enter \mu and that inserted, inline small Greek character mu survives to a PDF export, and presumably printing too.

With MS Word 16.78, one can enter a unicode sequence with pressing and holding the option key, clicking the + key, and then entering the unicode sequence (.e.g. 03bc). Word saves a PDF with the mu character intact.