When I change text in a draft the change doesn't say

After changing text in a draft, do you hit command-S or go to the File menu and hit Save? That should save the draft.

If not, can you show us what your Mailbox settings are in Mail menu -> Preferences

How to post an image in Apple Support Com… - Apple Community

You should cross out your email address for privacy.

Go to Window menu -> Activity menu to ensure Mail isn't stuck doing some other activity.

Make sure your Mail menu -> Preferences that the Drafts folder is setup properly.