Update to Catalina 15.0 or higher.

I normally use my Ipad or Iphone. Now I am starting use my MacBook Pro again as well. To install Adobe Pro on the MacBook, I need to update to at least macOS 15 or higher. I updated the MacBook Pro to macOS High Sierra 10.13.6 and from there was going to update to macOS Catalina 15.5. I get a message that going from High Sierra 10.13.6 to Catalina 15.5 requires an interim update of Catalina (?) 15.0, but Catalina 15.0 does not seem to be available for downloading from the Apple download service. Does anyone have any ideas. Thanks. Matt