Yes... many, many internal deployments are definitely using MS-SQL services. StackOverflow.com uses MS-SQL, for a prominent, public example. There are client libraries via ODBC or direct in many languages and platforms, including Node.js (mssql/tedious) and Rust.

As to where, AWS offers Windows as do many other cloud providers, including a significant portion of Azure VMs. Not to mention, that MS-SQL and SQL-Edge both run on Linux. IIRC, Azure Cloud SQL is also MS-SQL running a non-windows version. There's also Linux/x86_64 Docker images.

Aside: if you're willing to write a big check, MS-SQL replication configuration is far easier than pretty much anything else to setup and configure (UI based flows or scripted). While I personally advocate for PostgreSQL, I've used and mostly like MS-SQL fine.

That's really interesting, a lot of that is new information to me! Thank you for the detailed response, I appreciate it.