As the font name says, Finale Copyist Text is a text font (not a music font).

… selecting "abbreviate" in the menu for 2/2 displays blank …

If I understand you correctly, using the Time Signature Tool you need to set the time signature to 2/2, displaying as the abbreviated symbol for 2/2 - right?

The symbols for abbreviated time signatures are located in the music fonts.

The text font Finale Copyist Text is designed to work with the music font Finale Broadway.

Document menu > Set Default Music Font…

Set the Default Music Font to Finale Broadway, and the Time Signature Tool will let you display the abbreviated symbol for 2/2.

By The Way:

There is a useful context menu in the Time Signature Tool.

Via the context menu you can change the time signature to many commonly used time signatures.

There is a useful context menu in the Time Signature Tool.

The time signature contextual options are also available by right-clicking or ontrol+clicking using the Selection Tool as well.

Thanks all, it's reassuring this forum is still alive. My mistake was in assuming those characters would be included in certain  text fonts, which isn't too unreasonable given they appear in a "music" family e.g. Finale. Finale Broadway does look the best if I'm using Copyist for general text (thanks for the tip).. I find it better just to change the time font in the document options menu rather than the default music font because I prefer F Jazz for noteheads, articulations etc.