In the future you may need to delete posts out of your database. Regardless of whether or not Flarum has the features now or in the future. Here's a quick guide as long as you are able to use phpMyAdmin.
https://github.com/zerosonesfun/tutorial-phpmyadmin-bulk-delete/blob/main/phpmyadmin__how_to_bulk_delete_with_a_sql_query.pdf
If you like this tutorial and want one for your community explaining anything you'd like, I can create one in pdf, word, html, and powerpoint for you. All I ask for is a "coffee" in return (aka $5). You may contact me via wilcosky.com.