Re: "Mac 24 inch M1, 2021 and macOS Sequoia version 15.6.1. and macOS Sequoia version 15.6.1".
"After deleting emails, I go to my Trash folder and they are not there."
Thank you for your question to the community, and the details you thhoughtfully shared with us.
Keeping MacOS updated to the most recent compatible version often sidesteps issues that may arise.
Eg: There have been 4 updates to MacOS Sequoia since 15.6.1.
What's new in the updates for macOS Sequoia - Apple Support
says macOS Sequoia 15.7.3 is the most recent ... and
"This update provides important security fixes and is recommended for all users."
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Reminder: If you choose to update MacOS: It iis always wise to back-up youtr Mac first.
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Re: "Deleted email vanish and do not show up in the Trash folder when deleted from the Inbox"
If you are using MacOS 15.7.3 and still have the same issue:
- Sometimes there are more than one Trash and / or Bin mailbox-folder in the Mail sidebar
(Eg: You may need to check in the one for your eMail provider: (eg: may be one for Yahoo, one for GMaiil, etc.)
and / or
- You may want to check your settings to see what folder is set-up to receive deleted e-mails.
Eg: sometimes deleted, emails are set to go to "Archive" (or another folder you once chose)..
Change settings in Mail on Mac - Apple Support
Eg: says:
"In the Mail app 
on your Mac, choose Mail > Settings, then click a settings pane:
* Accounts": >
"Use the Mailbox Behaviours pane to change where draft, sent, junk, deleted,
and archived messages are stored."
