MacroKata is really good!
I'm not 100% sure, but I think I read about it on this sub anyway. I just wanna enforce that it's really good!
In my opinion, the teaching materials about macros are a bit "all over the place". The official book doesn't go into any depth. The reference is not very approachable. And then there's one exercise on exercism, which also seems a little ad-hoc.
MacroKata is the most systematic teaching material for macros I've come across! The first one that actually attempts to teach you how macros work and the theory behind it. And there are several exercises, each adding just a little bit of required knowledge to solve it. Baby steps - the best way to learn!
Note that this is still only about declarative macros, not procedural ones. I'm still keeping my eyes open for that.
If you know of any other great "systematic" teaching materials on macros (declarative or procedural), please do share!