I checked my watermarks in Classic v13.2 and found this-
-Most of my watermark presets were intact with their defined Font. (eg. Papyrus)
-Myriad Pro font was missing, not available, in the watermark editor font selector.
-Myriad Pro was not even installed in my Windows-11 system!
-I found the Myriad font files in a Lightroom folder and 'Installed' them to my system.
-Now they are available in the watermark editor!
What removed them from my system I have no clue.
Screen-clips are-
1) A search for fonts in folders-

2) Selected and INSTALLED those found from the search-

3) Fonts (Myriad Pro) previously missing now appears in the watermark editor (after a LrC restart!)

Regards. My System: Windows-11, Lightroom-Classic 15.4.1, Photoshop 27.8, ACR 18.4, Lightroom 9.4, Lr-iOS 10.4.0, Bridge 16.0.3 .