Hello,
You can change it from below method in sale order..(odoo default)

def _notify_get_recipients_groups(self, message, model_description, msg_vals=None):
    """ Give access button to users and portal customer as portal is integrated
    in sale. Customer and portal group have probably no right to see
    the document so they don't have the access button. """
    groups = super()._notify_get_recipients_groups(
        message, model_description, msg_vals=msg_vals
    )
    if not self:
        return groups

    self.ensure_one()
    if self._context.get('proforma'):
        for group in [g for g in groups if g[0] in ('portal_customer', 'portal', 'follower', 'customer')]:
            group[2]['has_button_access'] = False
        return groups
    local_msg_vals = dict(msg_vals or {})

    # portal customers have full access (existence not granted, depending on partner_id)
    try:
        customer_portal_group = next(group for group in groups if group[0] == 'portal_customer')
    except StopIteration:
        pass
    else:
        access_opt = customer_portal_group[2].setdefault('button_access', {})
        is_tx_pending = self.get_portal_last_transaction().state == 'pending'
        if self._has_to_be_signed():
            if self._has_to_be_paid():
                access_opt['title'] = _("View Quotation") if is_tx_pending else _("Sign & Pay Quotation")
            else:
                access_opt['title'] = _("Accept & Sign Quotation")
        elif self._has_to_be_paid() and not is_tx_pending:
            access_opt['title'] = _("Accept & Pay Quotation")
        elif self.state in ('draft', 'sent'):
            access_opt['title'] = _("View Quotation")

    return groups

You can change the “Sign & Pay ” button text in v18, but it isn’t Done from the regular email template. The walling comes from the Customer Portal settings and the Quote email template inside the Document Editor.

Here’s how you can change it to “View Quote ”:

1. Go to Settings → Customer Portal → Templates.

2. Open the Quote Template used for your quot emails.

3. Look for the button text field (usally under Call-to-Action Button or Primary Action).

4. Change “Sign & Pay ” to “View Quote ” (or whatver you prefer).

5. Save and reset a test email.

This is only changes the walling — the actual functionality of the portal status the same. Your customers will now see a neutral button introduce of something that can be like they’re being taken to pay for immediately.