You can create a lead without having a customer, but once you create a quotation you must have a customer.

One possible workaround is to have a "dummy" customer for Quotations and then change it to the real customer when you confirm the quotation.  It would be simple to create an Automated Action to block confirmation of a Sales Order if it's for the "dummy" customer.  You might also need to change the PDF report so it doesn't show the "dummy" customer.

I can provide a bit more detail if you think that's a viable solution.

thanks for your answer could you please explain more about your answer?

Hi,

You need to customize this workflow as it is directly available in Odoo.

Hope it helps