The source is there, just waiting for you to compile it. ;-)
If it's just a question of commenting out the unused features, then it's easy, right?
That appears to be wrong, unfortunately. :-( - or at least to my very quick trip through the source it does...
There's bits of it which give me hope it might be straightforward, such as checking which version of graphics.library is returned before assuming compositing is available, but then others which worry me, such as some of the dependencies.
Having a quick look, it seems that things like libcurl (first dependency I chose) require OS4+... So then you're into backporting all the dependencies too.
I don't know how much time it would take to port this to 3.9 or previous, but it's not a question of commenting out the bits that don't work as that would be everything.
Unfortunately my development for AmigaOS sorta stopped 16 years ago, and I wasn't doing anything nearly as complex as this.
But I would love to try to help get this ported. I think an analysis of what is needed would be a wise first step, and then a bit of a plan...