It works, showing a link and the full message in the Description, but only if there is a local calendar. Tasks aren't supported for some network calendars, such as Google CalDAV calendars in TB. Are you able to create tasks directly in your calendar?

I don't use any calendar, not even Thunderbird's calendar. I just add messages as tasks in my task list. When I clicked on a task, the edit window used to have a link to the original message over the description. Now it has disappeared.

What happens if you create a local Home calendar and just ignore it. Does the task editor now show the details?

There is already a calendar that I don't use, as you suggest, but the link to the message that used to exist in the edit window of a task (when it was converted from a message) has disappeared.

There is already a calendar that I don't use, as you suggest, but the link to the message that used to exist in the edit window of a task (when it was converted from a message) has disappeared.

I just tried it and it is still there for me on Windows 11 and Thunderbird 128.7.1

I give you a screenshot. I have Windows 11 and Thunderbird 128.7.1