The app's preset for @aol is IMAP already and has always been.
To OP:
How exactly are you deleting messages?
When an account's "how to delete messages" it set to "hide" -- then, if you select one or more in a message list, you should see an "cross out eye" icon, this is "hide".
Same icon in message view.
This is what you will want to use.
On the other hand -- the "other" two methods for deleting messages are still available, in message list and message view, under the "three dots" icon.
This lets you delete messages using your preferred (account's default) delete method, but still occasionally "move to deleted" or "delete now" some specific messages when you need to do exactly that (and not hide).
That one thing that comes to mind.
If you use swiping, then please check app settings -> swipe, and make sure that your swipe command is set to "the account's delete method" (in your case, it will resolve to "hide"), or just "hide" explicitly.
It is possible to set a swipe command to "delete now" or "move to deleted", even if you have accounts set to "hide" as their default.
Again, this is for flexibility, you can have both a "hide" and a "delete now" assigned to different swiping sides or positions.
So please check what your swipe commands are set to.
