I can't open the demo project with my Godot 4.3 editor. The demo and the entire code is made with Godot 4.4, so it shouldn't be compatible.
Heads up for potential buyers.
I have it working on 4.3 stable. I will reupload the demo just encase there is some small difference that's causing you problems. Did you open with 4.3 after getting the warnings about 4.4? I have been editing in 4.4 but I don't believe I added any specific code that should not be 4.3 compatible like typed dictionaries.
Edit: I reuploaded Grid Building v4.2.0 ~ All Packages (Requires Godot 4.3+)

I get these error messages with both Godot 4.3 and 4.4 (fresh downloads each)
https://imgur.com/a/IuRgnhZ