I don't use Grammarly because I read my work and that's how I want it. But if I do run something through Grammarly, it's set to British spelling anyway. It's annoying when they change it to US English... one recently changed some of it, but not all of it. So I had a story that read 'travelling' with one L (American) and favourite with a U (English). What a load of rubbish! I put the extra L in travelling because I refuse to have a ridiculous hybrid.