Itr due date extend?

It is very much likely to be extended this year due to new portal issues and glitches. They have no choice. 

However, as much as we know the habits of our elected representatives and their "pet bureaucracy model" the extension of due date is most likely not to be announced so early. Extension to due date may come by 20th September or in that week.

No notification till now... already extended to September 21

Likely to be further extended ...

I have filed B2B invoice in gstr1 of feb 2021 now during filing gstr1 of sept 2021 it comes in knowledge that that bill was cancelled now how to give effect of that cancel bill in gstr1 sept 2021 1) in sept 2021 gstr1 whether amend that bill by showing value as zero of that bill or 2) issue full amount credit note dated same as invoice date.