In odoo v16 email body you have to use this sysntex for dynamic content display and any other fields you can use {{object.name}} this sysntex

In Odoo v16, when creating email templates, you should use the following syntax for dynamic content display:

To display dynamic content:

To include values from other fields: {{object.name}}

By using these syntaxes, you can ensure that your email templates correctly display dynamic content and field values in Odoo v16.

we got a solution from the ticket we sent! I am including it below: 

After investigating the issue on a duplicate database, it seems that a Studio view was blocking the code view and Dynamic Placeholder options from showing.

To fix this, you will need to archive the inherited Studio view on the Email Template form view.

It seems that doing so only removes a blank "New Tab" that was added. Therefore, I do not think archiving the Studio view will not affect much and will allow the new features to work.

I attached screenshots from my duplicate to show the features are now present on for user XXX after I applied the steps.

Please apply these steps to your production database:
1. Go to the Email Templates > Open any template.
2. Open Studio > Go to the View tab > Click "Restore to Default View".
3. Save and close Studio.
4. Check that the features are present and usable for you.

I hope this helps, please let me know if you have any further questions or comments about this ticket.

from v16 (or v15, I don't know), email body is a qweb so the equivalent of ${...} of v14 in becomes : 

<t t-out="..."></t> in the body

{{object.name}} in the other fields

I found the solution here : https://www.odoo.com/fr_FR/forum/aide-1/email-templates-dynamic-placeholders-not-working-v16-223868

Use the keyboard only and it works

but it is still hard and not user friendly at all, at least with firefox and standard theme because your can't see what is your current item (it is not highlighted or something like that ! ).
My trick : So, I cope with that because at some point the list scrolls and I needed the last item in the list

este comando y al final 

Usa / este comando y al final de lista tienes el generador, sin embargo, aun no se como funciona, porque aun se ubica el campo y se le da enter, aun asi queda en blanco