First Draft
This is a test DM to myself. This was suggested as a way to create a post as a draft. I think this works only on apps that support some sort of copy, delete and post feature. Here goes...

Second Draft
OK, I'm back. This is an edit of my first draft. The feature to change a draft (DM) to final (regular Post) is "Delete and Redraft", found in the ... menu when you view your draft DM.

Final (visible)
The process all explained at https://fedi.tips/how-to-use-mastodon-and-the-fediverse-advanced-tips/