If, instead, you won’t do it and prefer to keep Bugzilla as the main issue tracking platform, could you tell us why?

Here are the reasons why: https://community.kde.org/Get_Involved/Issue_Reporting/Why_not_GitLab_Issues

The tldr is that Gitlab Issues is limited for users, developers and triagers compared to current Bugzilla, given the current KDE infrastructure. These are just technical issues. The moment Gitlab solves those limitations, KDE would gladly use it.

[...] since they’re right there by the code base.

Note the section "Bugs need to be filed against individual repos". At it stands right now, if a non-technical user finds a plasmashell bug, they can just go to "File a bug":

and they're greeted with this:

And then they can choose Plasma and then plasmashell, both with very descriptive text mentioning what should be reported there. It's not too bad to find the right place to report things, to be honest. And there's an "I don't know" field, which is great. :)

Finding issues can be a bit finnicky, yeah. But you can click on the search field in the first page, type what you want to find, click on Quick Search and you get a list of results based on your keywords, and you can also click on the Search button and then click on Simple Search to look for some keyword in a specific product. Once you know it's pretty simple.