Hi I find a solution for this issue by adding only 2 words

In settings->user interface->views, search for "Mail: Pay Now mail notification template"

Find and add "false and " like I write below in "bold" :

< t t-out="message.body"/ >
< div t-if="false and is_online and not record._context.get('proforma')" style="margin: 32px 0px 32px 0px; text-align: center;" >

So if you need to cancel your choice, you only have to delete "false and "

Best regards

for version 14.0

Remove Mail Invoice Button