@smokey My posts do have titles, in my functions.php I have modifyposttitle Which runs on wpinsertpost_data this adds titles and hence the slug (I guess😉) to posts without titles.

Intended for posts coming from micro.blog and AppleScript it seems to work in the WordPress post editor too if I don't put in a title.

I strip titles out again in the rss for posts intended for micro.blog (hopefully I'll change this to just status posts at some point). I think my approach is a bit messy😀.