P.S. regarding the search for already existing topics:

The search result pages linked with tags (like for ex. https://bugs.sogo.nu/view_all_bug_page.php?filter=6acdf537dbe37) are neither working. So it's also not possible to display posts / bug reports with a specific tag.

Tags on emails are not just a thing SOGo does.
Email taglist consists of all tags defined in SOGo plus the ones known to the IMAP server for that account/postbox.
You need both, when you use different clients with different taglists.
When you set one tag with one client, then you want to see that with the other client too.
And you want to be able to set them on both clients afterwards.

In order to remove unused tags, you first have to remove those old tags from all emails in this account, then tell the IMAP server to recreate its taglist.
Several IMAP servers don't have that functionality at all. For those you would need to create a fresh postbox and transfer all emails without those old tag into it, then switch accounts.
The one IMAP server I know which has this functionality, you have to issue a command on the server with admin privileges.
Obviously SOGo can do neither.

Just as info:
1) This is the official Bug tracker of SOGo up until version 5 including.
Which is stated so on the official Website for SOGo.
git is only used as repo for the sources, nothing else.

This will change with SOGo version 6, which is still in alpha stage.

2) You only get a read-only account on self service, because before there were Spammers hijacking this Bug tracker.
That lead to a lot of unnecessary work for the admins, removing that trash and blocking those accounts.
Therefore you have to write one email on the official mailinglist, in order to get write access for your account.

3) You only can search the Bug tracker, when you have at least an read-only account. This prevents bots from creating unnecessary load on the server.

PS:
In my humble opinion, if this is too much work for someone, then it probably is too much work to provide a good Bug report as well.

Thank you very much for taking the time to analyse and explain!

@ User feedbacks:

Imho, user feedbacks are very valuable, but most product or service providers don't recognize this and thus make "feedbacking" as hard as possible. This leads to unhappy or even switching users, and to buggy or suboptimal products (like a software) or services.

I'm also often confronted with excuses and blame games, just because someone obviously doesn't want to look for or apply a solution. This is neither helpful.

@ Tag issue:

Even knowing your explanation, from a SOGo users perspective, I shouldn't have to care about this technical background, imho.

Even if tags are coming from somewhere else or going to somewhere else (some IMAP or whatever), as a user I shouldn't have to bother and execute some server codes.

If I add a tag via SOGo, it should show up in SOGos tag list and email filters. If I delete a tag, it shouldn't anymore (even if it was coming from somewhere out there, or if some emails were tagged with it). Simple logic, no?

I analyzed the problem with the help of an AI for quite a while (so that I don't have to bother you and use a complicated bug report system), but found no solution. I executed commands via SSH to delete tags from emails, to look up tags in files on the server, to regenerate tag files, etc. - nothing helped. In the end, the capable AI (Gemini) had to admit that it couldn't solve the problem, and that it has to be solved by SOGo developers (btw, I'm using Mailcow dockerized + SOGo).

Despite some critique, my feedback is well intented, and I hope my ideas and viewpoint help to improve at least maybe some small thing to the better!

PS: The AI has also made me aware of tags within SOGo that shouldn't be changed, as they're used by other mail programs like mobile Thunderbird, or the like. As a user, I couldn't know this by myself, so I think these "standard" tags should either be blocked from changes, or there should at least be some warning or deblocking-necessity (via a checkbox or so) before being able to change them, no?