I have recently been looking at generating custom content entities and this lead to generating a minimal entity that would be useful on a Drupal site.
If you've ever used Drupal Console to generate a content entity, then you'll know what it generates a lot of files. There's all sorts of classes and configuration files generated that handle everything from generating lists of entities and forms for creating new entities.
This got me thinking about what are the minimal about of configuration to generate a usable content entity. This might be used to store some simple data or to attach to other entities through an entity reference. As it happens, setting up a minimal content entity takes just a single file.
Read more here: https://www.hashbangcode.com/article/drupal-9-creating-minimal-content-entity