Hi:

You can define a new security group and assign it only to the Manager(s). Then customize the Quotation view using view inheritance and add a "groups" attribute to the "action_confirm" buttons. As a result of this, only the Manager(s) will be able to see and click on the "CONFIRM" button.

You can hide the "SEND BY EMAIL" in a similar fashion by adding attrs="{'invisible': True}" to the "action_quotation_send" buttons in the view customization.

A nice question, as this functionality is already available as "Purchase Order Approval" and the same principle would be very useful in Sales.

A good solution can be found in the answer of the following forum:  https://www.odoo.com/forum/help-1/question/how-to-make-the-quotation-confirmation-or-approval-by-the-manager-not-the-sale-person-odoo-12-153504

See also:  https://twitter.com/fheodoo/status/1201678555219812352/photo/1

BR

Ricardo

Please see this module that helps to implement multi-level dynamic approval workflow for sale orders:

https://apps.odoo.com/apps/modules/15.0/xf_sale_flex_approval/

The module is available also for versions 13 and 14. If you need for older version, please contact me.