Is buying products from aggressor nations, such as America and Israel, considered showing loyalty to them and an act of apostasy, especially since many of these products are not necessities?

Islam has permitted dealing with disbelievers through buying, selling, and leasing, as long as the contract is for a permissible matter and does not involve showing them loyalty (muwalat) or apostasy. The Prophet, peace and blessings be upon him, and his companions dealt with them. However, if the Muslim ruler or scholars deem it obligatory or recommended to boycott the products of a specific country or company, such as when they mock the Messenger, peace and blessings be upon him, then it is obligatory to follow their ijtihad (independent reasoning) regarding benefits and harms.