OK, the compose window works now...
...but you may notice a lack of a Title...
...because that still doesn't work. I can click on the "Post title" entry, but I can't enter anything.
Let's see if it will post.
It does! That means: ((quick edit later)) AH HAH! I can edit the title in an existing posting. We have a work-around until Blogger gets a clue.
Update 2: as of Sunday, 24.June, things are working as designed again. Hurrah!