Excuse me, but I hope that this will serve to retro feed the answers given here to the cases. It seems to me a lack of respect, that the solution to my incident or requirement is to refer me to case 6425, when the solution to that case is "Please discuss on the mailing list if we should review our category list." This is called rallying the user. Thank you very much, but that is not my case and I think it does not enrich the use of Mantis

You are requesting a feature in MantisBT which is not available in current version.
If I understand right, you are requesting the same feature that another user requested before in 0006425.
Let me know, if your request is different from it.

We don't want to track the same request in different issues. It's better to have all discussion at one place. That's why we resolve the newer issue as a duplicate and set the reporter of the new issue to the monitoring list of the old issue.
So you will be notified whenever there should be a change of the issue.

This is our workflow to triage incoming issue https://www.mantisbt.org/wiki/doku.php/mantisbt:support_corner
This is certainly not

a lack of respect

Do you agree that I can set again to resolved?

Please confirm me. That is to say that the solution to this requirement does not exist? If so, please inform and proceed to move the incident to a resolved state.

That is to say that the solution to this requirement does not exist?

Right, Resolution of 0006425 is set to open.

Maybe using the following plugin is an option for you (use two custom fields instead of category and sub-category)
https://www.mantisbt.org/wiki/doku.php/mantisbt:plugins:linkedcustomfields
https://github.com/mantisbt-plugins/linked-custom-fields

Unfortunately this plugin does not work with MantisBT 2.x at the moment, but there is currently a user working on it, so maybe it can be used in a few days.
https://github.com/Maximus48p/linked-custom-fields