Is there a sin for not washing the ears in ghusl previously out of ignorance, and is it obligatory to repeat the ghusl or make up the missed prayers for the same reason?

One must wash the ears during ghusl janabah (ritual bath after sexual impurity). If someone performs ghusl but does not wash their ears, their prayer is invalid and must be repeated. According to the majority of scholars, all invalid prayers must be made up. If you do not know the number, continue making them up until your obligation is fulfilled. There is another opinion by Shaykh al-Islam Ibn Taymiyyah that does not necessitate repetition. You bear no sin for not washing your ears due to ignorance, as this is an issue whose ruling is obscure to the general public.