Mail app; Advanced account setting change not holding

In the Advanced Settings for my AOL mail account, I need to change the Mailbox Behaviors for the Deleted Mailbox. The iOS App allows me to select the appropriate Folder on the IMAP server, but the setting change does not hold, i.e. the change is not Saved.

Background: My e-mail account is an AOL mail account. Not my first choice, but Verizon stopped supporting my e-mail address and I was forced into AOL because they agreed to preserve ....@verizon.net mail routing. I am running in IMAP mode, because I access my e-mail from my laptop (Windows 11, using the Thunderbird mail app) and my iPhone (iPhone 13 Pro Max, running iOS 16.0.2)

The Problem: Thunderbird seems to have a problem with the way it handles the AOL mail server folders, in that the Trash folder is in the following structure:

By default, messages deleted on my iPhone end up in the 2nd level Trash folder (not the Trash folder). If I empty the Trash, then any messages in the Spam folder could get deleted before I have a chance to check them. The Spam detection is performed by AOL and does a reasonable job, so I don't want to change that aspect. So I created the Deleted folder and configured Thunderbird to put deleted messages there.

In iOS under Settings > Mail > Accounts > AOL > Account > Advanced

It is possible to adjust the folder for the Deleted Mailbox function by clicking its >, which leads to

Now my desired configuration would be met by selecting the Deleted folder under the currently selected Trash folder. BUT although it is possible to move the Check-mark to that Deleted folder by clicking, I have found that this selection is NOT remembered. There isn't a Save button, so I have not found the secret to making the configuration change permanent.

Any ideas on how to fix this would be most appreciated.

Regards, Mike D.

[Images Edited by Moderator to Remove Personal Information]