H1B Transfer after approval

I am waiting for my H1B approval this year after lottery selection, i have the receipt notice I797C, i am planning to switch my employer in next 20 days.

In case i switch it before the approval, would my next employer be able to transfer my H1B based on I797C i have? Or would it require the approved I797A/B.

In case i don’t have that after i left, what are the chances of getting it transferred and what is the work around for that.

If this is possible, what documents would be required?

Thanks in Advance

They would need current H-1 to be approved first. If the current employer withdraws the petition while it is pending, then you are out of lottery. If they don’t withdraw the petition and it is eventually approved, then new employer should be able to avail it for cap-exempt purposes.