Is rectification request tab enabled on new portal??

apply before jurisdictional AO

Yes, in fact I guess in the faceless scheme it has been mentioned that rectification rights are with jurisdictional AO. Therefore, you may apply physically by way of letter alongwith all the supporting documents before the jurisdictional AO for the relief.

No ,  only it will show notice served to you, reprocess return  tab is on , means they will recalculate as per return filed, any mistakes done , actualy you need to file revised return . 139(5), if you done any mistake in 21-20 AY one can file  revised return normal way but for previous years tab is not on, so need to wait, I understand any mistake done possible to rectified  last 4 years time.