https://www.macg.co/logiciels/2019/09/yummy-ftp-tirera-sa-reverence-avec-macos-catalina-108491
Yummy FTP will stop working on macOS Catalina due to the use of 32-bit components. The creator of the app, Jason Downing, died suddenly last year, according to a message posted by his family on his Twitter account.
Nobody seems to have resumed the development of this FTP client. The app has been removed from the App Store and its website is offline.