I have a Mac Mini with Catalina. (Just for perspective) I too had problems (I wonder if you people have not solved this) I had this issue. I tried opening things from the download Folder...No. Other folder, No. So I moved it to the one place where things get installed. I put it in the Users folder under my name. I dropped Hero Designer in here. This is where the Music folder is at. From inside Hero Designer, I created a folder here and in THAT, I put any new characters that I created. I put pictures there too, since I could not access pictures from any other folder. (other than Hero Designer) This is what works for me. I hope this makes sense.