How can I access grayed-out fonts in Font Book on macOS Sonoma 14.6.1?

I have an extensive font collection that I can't seem to access with Font Book. When I go to add a font, the fonts I want are grayed out as in not available. Many of these fonts are from ITC, Adobe, etc. Is there a way to access these that I am not aware? Thinking that I may have to buy a font management app. Can anyone comment? Sonoma 14.6.1

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