These are the official rules:

1. If you are new to Godot, we suggest using version 3.2 for a stable experience.
2. Reusing existing code and assets is allowed. - No re-skinning of games made outside of the jam. - A majority of the code and/or assets must be made in the jam's time frame.
3. This is an exclusive jam which means that entries made to both this jam and others will be removed unless otherwise allowed by the organizers (Stern Flowers).
4. Follow the theme.
5. Have fun!

None of these rules state that you have to use the Godot Engine, so I might use unity for this game jam.

Also to #1: it is better to use version 3.2.1

This is a game jam that is for Godot Engine users. If you'd like to use Unity, please join another jam.

lol