@David_Henriques I believe this is expected behavior. You’ll see in this post that Archived Projects became searchable at the end of 2019: Searching Archived Project Titles - #37
One way to avoid Archived Projects showing up in a search is to move them to their own Team. This way you can use the “In teams” filter within the Advanced Search and exclude the Team of Archived Projects. The issue being there isn’t currently a means to search items NOT in a specific Team. That option as well as other creative solutions are all part of the #productfeedback here: Option to exclude archived projects/tasks from search