will they allow me to write jee advanced 2020 if iam not able to provide gen ews certificate before 26 sept?
JEE Advanced authority will allow you to write the exam but they won't consider you as an EWS category holder. You must upload the original EWS certificate issued on or after April 1, 2020 before 26 September, 2020, 5 PM.
However you may upload the declaration in lieu of GEN - EWS during appliction. If you are unable to upload the fresh certificate before stipulated date and time, the benefit of GEN-EWS certificate will be withdrawn.