Merriam-Webster dictionary shows slightly different definitions of both the terms. However, Urban-dictionary shows the definition of Anti-nationalist similar to anti-national in Merriam-Webster dictionary. Also, different sites show different meanings.

Can anyone explain the difference between both the terms to a non-native English speaker?

Edit 1: Oxford dictionary has only the meaning of Anti-national. So, is it possible that Anti-national is preferred term in British English?

Edit 2: Check this link to see how Anti-national is used in Indian English media: https://m.economictimes.com/news/politics-and-nation/view-will-the-real-anti-national-damaging-bharat-please-stand-up/amp_articleshow/61515366.cms