@marcan apparently squash on merge is an option of the project https://docs.gitlab.com/ee/user/project/merge_requests/squash_and_merge.html#configure-squash-options-for-a-project and I guess that's not what KDE folks prefer.

According to docs https://docs.gitlab.com/ee/topics/git/git_rebase.html#rebase-a-branch the interactive merge must be done on command line (as you did).