This study is testing a new blood thinner called asundexian to see if it can prevent strokes and blood clots in people with atrial fibrillation, a condition with an irregular and often rapid heartbeat. Researchers are comparing asundexian to an existing medication, apixaban, to see which one works better and has fewer side effects. Participants will take either asundexian once daily or apixaban twice daily for 9 to 33 months, with regular check-ups to monitor their health.