A Flarum extension. Adds a BBcode button to the Composer toolbar. But, get creative. You may use it for other purposes as well! The admin settings allow you to input a custom BBCode tag (i.e. [jump][/jump]), or really any text, add any Font Awesome icon for the button, and adjust where the cursor appears in the editor after pressing the button. This has only been tested with Flarum's default editor. It should work with the wysiwyg rich text editor, but you will see the raw BBCode until you post.
This is great with the default editor paired with the preview extension.
Install with composer, and after activating, input and save settings.
composer require zerosonesfun/flarum-bbcode-button:"*"
composer update zerosonesfun/flarum-bbcode-button:"*"
php flarum migrate
php flarum cache:clear
Deactivate, tap the purge button (cleans up the database), then run this composer command:
composer remove zerosonesfun/flarum-bbcode-button
(notice how quick it is to add your favorite or complex custom BBCode)