I also have ancestry from several different countries (all European).
I have a pretty good idea of my ethnic origins, at least in recent centuries, because I am third-generation American on one side, fifth-generation on half of the other side, and pre-Revolutionary American only the other half of one side (and that is most if not all English and Scots-Irish). I know where my immigrant ancestors were from (at least which country).
I have taken DNA tests from 7 companies. They disagree a fair amount on ethnic breakdowns (and some have sent revised versions significantly different from their earlier version). 23 and Me, Ancestry, MyHeritage and FamilyTreeDNA got it mostly right with minor exceptions. Living DNA got it somewhat right. CRI Genetics got it less than half right. GPS Origins was totally weird--all kinds of strange categories I could not possibly be descended from.
Instead of mutt or hybrid, how about American?
Most of the findings came from Scandinavia, Northwestern Russia, Iceland, basically Vikings.