I have been working with SharePoint for the better part of 15 years. During that time, I almost always installed SharePoint in a domain environment where the Application Server(s) and Database Server(s) were within the same AD domain. I am increasingly seeing use cases where SharePoint could/should be in a DMZ and simply having SharePoint utilise a SQL server cluster (deployed in a different domain, for example).
Historically Microsoft's support for SharePoint services to authenticate to SQL utilising SQL authentication has not been very well documented. The "support" was typically limited to a subset of services (e.g. a Content DB). And the wider SharePoint farm (and services) still needed to be deployed within the same domain at the SQL server.
Can you point me to some documentation/article that outlines how to install SharePoint Subscription Edition where all of SharePoint is authenticating to its SQL backend using SQL Authentication (rather than Windows authentication)? Does anyone have any experience doing this and stories/lessons you can share?