GST Registration Cancelation in current month

Hello Experts

Client wants to cancel GST Registration Voluntary due to shut down of Main business activity.

1. GSTR1 Iff & GSTR 3B Filing Quarterly basis.
2, Having Sales and Purchase in Current month also.

Query:
1. Is it possible to  filing for GST Cancelation in May 23 month also or Compulsory  to wait for July Month Quarterly Filing?

2. If Cancellation possible in May month, How Customers will get Input credit of sale invoices issues and How client will get Input ITC?

Please reply.