If you have no outward supplies but have inward supplies for July 2023, you should file a nil GSTR-1. For your GSTR-3B, you need to report your inward supplies and check GSTR-2B, rather than filing it as a nil return. GSTR-2A is auto-generated and doesn't require manual filing.
29 July 2023
No outward supply then file GSTR 1 return as NIL...
Have inward supply then file GSTR 3B return based on Your inward supplies and Check GSTR 2b also...
Don't file GSTR 3B as NIL return...