As far as I know Gleam is the only strongly typed language on BEAM, which is important to me since I don't like dynamically typed languages. But of course Elixir gets optional types now.

There is also:

Purerl - Erlang backend for PureScript, a few folks are using this in production - https://github.com/purerl/purerl

Caramel - Ocaml for Beam, seems dead - https://github.com/leostera/caramel

and more probably dead projects at https://github.com/llaisdy/beam_languages

Is that the only difference?

It can also compile to JavaScript (instead of the BEAM) so you can use the same language for backend and frontend work.