Probably the OS keyboard shortcuts collide with the ones in the extension's. You can modify the shortcuts from your browser. If the filling does not work, the issue seems that you are using incorrect URL's in your entries. You must define them with the simplest form possible. For example a page with URL https://www.example.com/login_page/ works great with entry URL defined as https://example.com. That works as a wildcard for https://*.example.com/*.
For Debian it's recommended to use the PPA or AppImage because the default repository often offers an old KeePassXC version.