User blog comment:Tildeman123/A tutorial on how not to hate UCP/@comment-46542982-20201001125759/@comment-28720561-20201002224342

You can enable it by going to your preferences on any UCP wiki and select Source editor under Preferred editor in the editing section. I believe you can use wikipedia:MediaWiki:Gadget-legacyToolbar.js to enable the legacy toolbar and have it appear by disabling the Enable the editing toolbar option in the Editing tab (haven't tested it out yet). Here is the tutorial if you want to experiment with the legacy toolbar: wikipedia:Wikipedia:Legacy toolbar