This module exists to get around the 50 page limit defined in the JSON API Drupal module by extending the EntityResource service and overriding a couple of classes and functions. There are plenty of valid points on why you would want to do this and why you shouldn't. See this discussion.
To use:
Simply change SIZE_MAX in src/Query/CustomOffsetPage.php to whatever you'd like. I've set it to 500 here since I'm using the API internally.
In the future, may want to add this as a configurable option in the UI.