Regarding temporary GST registration

If OPC is doing taxable supply of goods or services occasionally then it will consider as Casual Taxable Person, then the company have to take compulsory registration under Section24 of CGST Act, 2017.

No.
Casual Taxable person u/s 2 is the person who occassionally run the business and who dose not have fixed place of business.
As per the incorporation process of OPC, each compnay is incorporated only after Registered Office.
so registered will be treated as Fixed Place of business hence it cant be treates as casual taxable person.

“Casual taxable person” means a person who occasionally undertakes transactions involving supply of goods or services or both in the course or furtherance of business, whether as principal, agent or in any other capacity, in a State or a Union territory where he has no fixed place of business.
what should I mean by 'agent or in any other capacity'