"Additionally, a theme will be announced at the beginning of the jam period, and so you're encouraged to link that to your game as well!"

Do we have to follow the additional theme too?

"so you're encouraged to link that to your game as well!" sort of implies its optional, is it?

you have to make a game with the theme that is announced at the start, you don’t have to follow the geometric shapes theme it’s just there as a suggestion