When you install software from the Debian repository, it does not always come up with the latest version. It adjusted with its own software release schedule. Any latest software usually comes first into testing/unstable categorisation, if already mature, the maintainer will move the specific version of the software into a stable release which will be readily available with apt install.

Debian repository does have the latest version of Electrum 4.4.6, but it hasn't yet on the stable release, so you need further configuration to install the latest version.

I suggest instead of changing your system-wide installation sources, you better manually install Electrum with its own installation tutorial. Go to https://electrum.org/#download, on "Installation from Python sources" go ahead with "Install with PIP:"