Hi,

After upgrading to Odoo 19, the frontend error when accessing the Discuss app occurs because the system cannot find mail.action_discuss in the actions registry. This happens because Odoo 19 has restructured the Discuss (Messaging) module, and the old window action mail.action_discuss has either been removed or renamed. Menu items in the frontend that still reference this action will trigger a KeyNotFoundError since the action no longer exists.

To resolve this issue, the menu item needs to be updated to point to the new action used in Odoo 19. This can be done by navigating to Settings → Technical → User Interface → Menu Items, finding the Discuss menu, and changing its action to the appropriate client action for messaging. Odoo 19 uses OWL components and client actions instead of traditional ir.actions.act_window for many apps, including Discuss.

Alternatively, if backward compatibility is needed, you can create a new XML record to define the missing action. For example, you can register a new client action with tag="mail.messaging_frontend_action" and update the Discuss menu to reference this action. After making these changes, it is important to clear the cache and reload the frontend so that the new action is properly registered and the Discuss app works without errors.

Hope it helps

There is no upgrade available yet for Odoo 19.

It is not possible for anyone to upgrade to Odoo 19 - we are in the early stages of testing the upgrade scripts for Odoo Online Customers (only) and plan to release the upgrade scripts for other deployment options in November (providing testing goes well for the first several thousand online databases and odoo.com later this month).

You have been misinformed / have misunderstood how upgrades work.

Review https://www.odoo.com/documentation/19.0/administration/upgrade.html

The official option from Odoo for the Enterprise Edition (when available) will be at https://upgrade.odoo.com and the Community supported / Odoo Community Assocation option for the Community Edition (when available) will be at https://oca.github.io/OpenUpgrade

The OCA option normally takes much longer to be available - you can review the status of their upgrade to Odoo 18.0 and see that not all models are available yet.