**Steps to reproduce:**
- Go to the chatter of any record
- Click on `Send message`
- Click on `Full composer` icon on the bottom right
- Prepare an email with custom subject / body
- Click on `Send Later` and set the scheduled time
- Mail is not sent on scheduled time

**Issue:**
For the timing issue, as the mail is sent by a cron job it obtains a context with `mail_notify_force_send` set to `False` due to the function `_get_eval_context` of `ir.actions.server`.
```
""" Override the method giving the evaluation context but also the
context used in all subsequent calls. Add the mail_notify_force_send
key set to False in the context. This way all notification emails linked
to the currently executed action will be set in the queue instead of
sent directly. This will avoid possible break in transactions. """
```

This context override the `force_send` value used when sending emails notifications. Everything is created properly but the mail is not sent directly and goes to the email queue manager (where it needs to wait until the next execution). This means that the time given previously is not explicitly used to send the mail and the mail is delayed (which doesn't seem to be the expected behavior).
```
if force_send := self.env.context.get('mail_notify_force_send', force_send):
    force_send_limit = int(self.env['ir.config_parameter'].sudo().get_param('mail.mail.force.send.limit', 100))
    force_send = len(emails) < force_send_limit
if force_send and (not self.pool._init or test_mode):
    # unless asked specifically, send emails after the transaction to
    # avoid side effects due to emails being sent while the transaction fails
    if not test_mode and send_after_commit:
        emails.send_after_commit()
    else:
        emails.send()
```

**Fix:**
Overwrite `mail_notify_force_send` value when posting the scheduled message in the cron job.

related: https://github.com/odoo/odoo/commit/df18d5257cef737f3e1d245a8b85769e1fe1a032

opw-4700253

---
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Forward-Port-Of: odoo/odoo#219475
Forward-Port-Of: odoo/odoo#211515