you can say that the difference is in timing when we use ف, there is a short period separating actions for example جاء أحمد فعلي ... Ahmed came then Ali The accurate meaning is that Ahmed came first and Ali was just behind him so they are not together but just behind each other but ثم indicates that there is enough time between actions for example جاء أحمد ثم علي .... Ahmed came then Ali Ahmed arrived and may sat down, eat and talk then Ali came that's it I hope I managed to enlighten you😊😊

Beide bedeuten (dann) , und werden gebraucht um Ereignisse zeitlich anzuordnen. فـــ heißt eher (darauf anschliessend). Also ohne Zeitspanne. ثم heißt eher (dann) . Nach gewisser Zeit.

ف :نتيجة لفعل ما ثم :ترتيب أحداث