Thank you for your interest in Kali but this is not a bug report. It looks like that you need help and guidance to perform some task. We have community support forums on http://forums.kali.org or on IRC with the #kali-linux channel on irc.freenode.net), please post your questions there.

I have no problem setting up the proxy in Kali. My problem is that the application does not appear to configure it manually. Going to the Menu / Configuration, Manual Proxy Configuration appeared, but now it is not, only the Advanced Network Configuration appears. I don't know if you're understanding me, that's why I added the sample video.

I'm sorry but even with the video, I'm not understanding what you mean. We have switched to Xfce and we don't have the same features. Our GNOME setup has a GNOME Shell extension "gnome-shell-extension-proxyswitcher" and there's no equivalent in Xfce, at least not in the default setup that we provide.

Are you complaining of the fact that this feature disappeared ?

As you figured out, there's still a way to configure a proxy through network manager. But really, there's no bug in all this. So I'm not sure of the purpose of this bug.

This report has been filed against an old version of Kali. We will be closing this ticket due to inactivity.
Please could you see if you are able to replicate this issue with the latest version of Kali Linux (https://www.kali.org/downloads/)?
If you are still facing the same problem, feel free to re-open the ticket. If you choose to do this, could you provide more information to the issue you are facing, and also give information about your setup?
For more information, please read: https://kali.training/topic/filing-a-good-bug-report/