when engineering classes starts for Freshers 2021??
As per now all the admissions aren't done. So you have to wait till the admission process is complete and the verification are done then online classes may start. Now depending on the covid scenario the nature of class will dependent that is online or offline.
Now if you are asking for private college then also there are no finite deadlines available till now. So you may expect the classes to be start from August may be or from July 2nd week,2021.
I hope this answer helps. All the very best for your future endeavors!