I downloaded latest Keyman keyboard, then after downloading Amharic font I get the error message:
There is no application set to open the document “gff-amh-powerpack-7.kmp"
Sorry that you’re experiencing issues installing that keyboard.
Could you try downloading and installing the Amharic for Keyman Desktop and seeing if that works for you?
It sounds like you may be using macOS? If so, follow the steps at https://help.keyman.com/products/mac/1.0/docs/start_download-install_keyboard.php#install_folder to install a keyboard.