H1B transfer before joining employer A through which petition was approved

If I get H1B petition approved through employer A, Can I transfer it to employer B before Oct 1st and without working for employer A at all?

I am actually trying to find more than 1 employer to sponsor my visa but at the end I only intend to work for only 1 employe X who is also sponsoring my visa.

Yes, that is possible. Another employer can file cap-exempt petition for you once your petition is approved. The new petition cannot have a start date prior to Oct 1 though.