A system plugin to customise TinyMCE beyond what Joomla lets you do.
WARNING! This plugin is meant for expert users. You can very easily break the TinyMCE editor or override Joomla's editor profiles if you're not careful.
How it works
Install the plugin and enable it; it appears in the plugins manager as “System - TinyMCE Configuration Modifier”.
Edit the “System - TinyMCE Configuration Modifier”.
The only option is an editor field where you can paste a JSON document with TinyMCE configuration options. Please consult the TinyMCE configuration reference.
IMPORTANT! At the time of this writing, TinyMCE has published version 6 of their editor but Joomla 4 is only using TinyMCE 5. Please remember to select “TinyMCE v5” in the drop-down of the TinyMCE documentation to view the information which is relevant to the TinyMCE version Joomla is using.