Whatever it is it's pretty deep in the weeds. It looks like the intent is for most users to be unaffected; non-AWS cloud providers to be unaffected; even AWS's Elastic Cloud to be unaffected; but AWS has to stop doing something with specific regard to Elastic Search and I can't figure out what it is.
I think the change that you can’t modify the code and use it yourself in production is a big change that is glossed over. ES is now free as in beer. You can look at the code but you can’t touch it or change what it does.
Edit: I was wrong about this. The license itself does not say this, but the blog post seemed to indicate that it was a change. I think it’s an exclusive inclusive or problem.
[0] https://www.mongodb.com/licensing/server-side-public-license
See 2.2 Restrictions: https://github.com/elastic/elasticsearch/blob/master/license...
With the dual-licensing you have a choice of Elastic license or SSPL, but they both have terms you might not like. And if you use the binaries you automatically use the free as in beer Elastic license.