First, create a custom module that inherits from the crm.lead model and include the following code:

from odoo import models, fields, api, _
from odoo.exceptions import UserError

class CustomCrmLead(models.Model):
_inherit = 'crm.lead'

def action_set_won_rainbowman(self):
if not self.quotation_count:
raise UserError(_("This opportunity cannot be marked as 'Won' until a quotation has been created."))
return super(CustomCrmLead, self).action_set_won_rainbowman()