The site is still accessible via wayback machine. Unfortunately little information be learned from it, apart from a link to a site with pseudo-code which reportedly served as the foundation. Would have really liked to see and read some more Godot specific implementation detail but alas.
Sorry, I did not have the capacity to maintain a website and underestimated the amount of work it takes to make a good quality blog.
Maybe the sourcecode helps you out, but be sure that it is not polished and there might be some "code smells"
https://github.com/codingvessel/boids here you go, it is based on godot4
EDIT: Im not quite sure if this sourcecode is uptodate, but it is what I have access without going out of my way. The sourcecode was written on a laptop which I didnt use for 2 years.
It should be enough to serve as a starting point to get it going, the dynamic adjustments with the menu are missing I think, but that should be the easier part.