I am not sure it is one of the largest projects.

The reddit subgroup has 300 members: https://www.reddit.com/r/themirrorspace/

The YouTube channel has 700 subscribers: https://www.youtube.com/@TheMirrorEngine

This doesn't come across as that big of a project in terms of user base.

For example, this Godot-based game on Steam has 12K reviews. It is definitely much bigger than The Mirror: https://store.steampowered.com/app/1637320/Dome_Keeper/

And another with 24K reviews: https://store.steampowered.com/app/2218750/Halls_of_Torment/

(Also is the guy in the video okay? His eyes are really red.)