Is this a Word document that you have opened in Pages? If that is the case, when Pages translates the document into .pages format, it requires that the internal Word document font references be physically installed fonts in macOS to avoid font substitution with its replacement font de jure (probably Times or Times New Roman). Unfortunately, the explicit font name reference must be installed as for instance, an EBGaramond-Regular reference will not match an installed Adobe Garamond (AGaramond-Regular) font.
I am running macOS 11.6 and I have no Garamond font located in /System/Library/Fonts, /System/Library/Fonts/Supplemental, or /Library/Fonts locations. All of my various Garamond OpenType or TrueType collections are in my local ~/Library/Fonts folder because I put them there. This is also a location that the operating system also searches for installed fonts and they become automatically available to your applications.
Here is the dafont free download page (click the adjacent green download button) for 22 typefaces of the OpenType Adobe Garamond font. All fonts are in an Adobe Garamond folder. Just move that folder to /Users/username/Library/Fonts folder and hopefully, you are done.