The Inline Formatter Field module allows site builders to template and style entities with a field. This module will create a new field type called "Inline Formatter" which is a boolean which can render HTML/twig when checked. The format can be configured by a site builder using the ACE Editor for a better editor experience.
It is recommended to use the Inline Formatter Display submodule, which essentially, gives you a way to make an entity bundle twig template without the need of actually adding files, changing a theme, or creating a child theme. You can add whatever HTML/twig you like to an entity's display.