I live in the United States and some of my non-Muslim relatives have bought me certain clothing items as gifts. I would personally never choose to purchase these goods myself to boycott their companies because of their support for the occupation of Palestine. Most often, these products are made in countries other than occupied Palestine but there is no question that some of their money (which I did not spend myself) goes to support a company, which in turn supports the occupation of Palestine, even if it is simply through political lobbying. If I wear this type of clothing and pray in it, is my prayer nullified or diminished?

Your prayer is not nullified.