Mac mini OS 13.2.1, Font Book does not reinstall missing font
I have been using two 3rd party fonts for several months on my Mac mini. During a routine upgrade, the fonts disappeared from Font Book. I re-downloaded the identical files from the original sources, but when I tried to reinstall each I received a pop-up message stating that Font Book had failed to install the font and that the usual cause was a lack of information in the file. In addition, I have had the same failure to install two other fonts I wanted to use for a presentation. I have followed suggestions made to others about different means to copy the font files into Font Book to no avail. I have restarted the Mac twice. I am at a loss, I am quite fond of the fonts. It occurred to me that I might reinstall Font Book, but I haven't found a source for a new copy.
Mac mini, macOS 13.2