Installed v11.0.103-2 using these instructions for Debian, and installed a keyboard but doesn’t show in keyboard dropdown.
Then installed v15.0.235-1 from same site, install seemed to work ok but km-config --version still says v11.0.103 and still keyboard doesn’t show in dropdown.
Then tried using a deb package keyman_15.0.235-1_all.deb but that gives error Dependency is not satisfiable: python3-keyman-config(= 15.0.235.1)
Did you manually download the .deb package from Debian? In that case you’ll also have to download and install python3-keyman-config and libkmnkbp0-0 (and possibly some other dependencies).
Also make sure that ibus is running. You can start it by running ibus-daemon -d. You might have to reinstall the Keyman keyboards you already installed.