You need to add the field to the model by overriding it..something like this:

from odoo import models, fields, api 
class WebsiteSaleOrderExtraInfo (models.Model): 
    _name = 'sale.order' 
    _inherit = ['sale.order'] 
    
    x_pickup_date   = fields.Date (string = 'Pickup Date', required = True)    

Within your view you will also need to allow the field to be whitelisted in the Web (this caught me out for a long time)

<! - Allow field to be whitelisted in web forms -> 
        <function model = "ir.model.fields" name = "formbuilder_whitelist"> 
            <value> sale.order </value> 
            <value eval = "[ 
                ' x_pickup_date ' 
            ]" / > 
        </function>