I've switched to Science United, having reached the limit of my tolerance with World Community Grid after 16(?) years. Their old management was bad but the new management managed to make it worse which seemed impossible. I'd like to remove that project from the BOINC manager but the "remove" button is greyed out. I take it that there is some magic required to remove a project forcefully but I'm not inclined to do all of the research to do it on my own. Can someone give me a clue about killing all traces of this abominable thing?

Yes, you can visit the project page (https://scienceunited.org/su_user_projects.php?project_id=22) and click "exclude".