Update April 22nd – to resolve this issue, go through the discussion, test Playground with the plugins that were mentioned, run a few SQL queries with the discussed syntaxes, and confirm it works. Also, with BBPress I my thread replies were stored in the db but were not visible on the website. Let's confirm this is also an issue in vanilla WordPress. If it isn't, let's figure out what's wrong with Playground.

Milan Petrovic said on Twitter:

and a lot of stuff related to MySQL not working at all, most likely because they have been disabled on the MySQL instance they are running.

most plugins don't work due to database issues or plugin requirements (you can't test any extension for WooCommerce or plugin for bbPress...).

Let's investigate this.