Turns out most clones are broken in one way or another. For example, the Digital Ocean S3 Clone forgets the file Mime Type, so our brotli compressed JS is served as plain text and it breaks Discourse completely. So there is no big howto guides, because the experience was awful as a few months ago and everything is changing very rapidly.
I plan on doing a complete check on the ScaleWay offering next week, and write a #howto if it works.
I can’t wait to read this documentation 
Very interested as well. I attempted to make it work on Rails with ActiveStorage, to no avail.
I have a pending PR before I can publish the guide at
https://github.com/discourse/discourse/pull/9481
I assume almost all S3 clones who use minio under the hood, like Digital Ocean, will need this.
This worked for me (thx!), while just setting the s3_endpoint trivially didn’t.
Needless to say it’s still broken, and clearly setting just the endpoint isn’t enough (this is common sense when integrating with S3).
The proper fix would be to allow customizing the region beyond the hard-coded amazon values in the UI.
Also, an option to use path for bucket is lacking, and this is a useful feature for the custom S3 integrations.
The supported configuration for Scaleway lives at Using Object Storage for Uploads (S3 & Clones)