I never call myself "mixed" ever. I will just say where my parents are from, no need to use the term "mixed". I am just both. Sometimes I will just say I am Nigerian/black, if it is a debate about Africa/black issues. No need to say "mixed". I am still West African/black. And sometimes my black part is irrelevant, when I need to check a zionist, and it is about some Arab issue.
Maybe I am lucky because Arab and brown skin/being black does not X eachother out, so I can easily say I am
just Palestinian, if I felt like it, but if I went around saying I was Swedish or Polish, I think I'd get a side-eye or two.
Just don't see the need for the category "mixed", it sounds like you are a new race. You just are both. Way more convenient.