Historically mongodb uses AGPL. A while ago they changed the license to their own SSPL, which does not satisfy the OSI open source nor the FSF free software definitions, in order to prevent cloud providers from offering managed mongodb offerings which would compete with mongodb atlas.

I do not know about OSI but SSPL most certainly fits the FSF free software definition.

It does not by my reading. It violates freedom 0 - "The freedom to run the program as you wish, for any purpose."[0]. You cannot run the program for the purpose of offering a cloud version.

[0] - https://en.wikipedia.org/wiki/The_Free_Software_Definition

Sure you can, just like the AGPL versions of mongodb. You just need to follow the terms of the license.

In this case how is Oracle different ? You can use it for any purpose... just follow the license.... which requires selling kidney, or two...

Still AWS and DigitalOcean offer managed MongoDB, am I missing something ?

AWS DocumentDB is mostly compatible with MongoDB, but isn't actually Mongo. When we migrated from Mongo to Document there were quite a few queries that failed to run, and we weren't even using complex features. Some indexes also failed to work in some queries.

Yes. AWS Has RDS Oracle Too It is different from Open Source where anyone could build DBaaS solution without any permission from the vendor.