Buttons inserted in Form "blank" are not rendered in email clients

Mautic 4.3.1
nginx: 1.16
PHP: 7.4
MariaDB: 10.3.32


The “blank” layout of Forms, when adding buttons (Send, Subscribe, etc) when sending emails from Mautic, the button is not rendered and is shown in text mode with link. This happens only with the “blank” layout, because “Paprika” and other layouts do render the buttons in Gmail, Hotmail…

There are threads about this on this forum, from previous versions:

In Mautic 4.4.0 this layout bug persists and there is no PR on GitHub where a solution to fix it has been proposed.

Does anyone know about this “bug” or is it something specific?