You can do it, but with a little of code.
Create a method like this, calling the rental action:
def action_view_rent_quotation(self):
action = self.env.ref('sale_renting.rental_order_action').read()[0]
action['context'] = {
'default_is_rental_order': 1,
'search_default_from_rental': 1,
'search_default_draft': 1,
'search_default_partner_id': self.partner_id.id,
'default_partner_id': self.partner_id.id,
'default_opportunity_id': self.id
}
action['domain'] = [('opportunity_id', '=', self.id), ('state', 'in', ['draft', 'sent'])]
quotations = self.mapped('order_ids').filtered(lambda l: l.state in ('draft', 'sent'))
if len(quotations) == 1:
action['views'] = [(self.env.ref('sale_renting.rental_order_primary_form_view').id, 'form')]
action['res_id'] = quotations.id
return action
Then add a button like this:
<xpath expr="//button[@name='action_view_sale_quotation']" position="after">
<button string="Rentals" class="oe_stat_button" type="object" name="action_view_rent_quotation" icon="fa-retweet"/>
</xpath>