User blog comment:MisterWoodhouse/The first Unified Community Platform release is now live for NEW wikis/@comment-26542627-20200312171300/@comment-24155515-20200314141321

I got the standard source editor (or, well, more visually aligned with MediaWiki's latest edit page code, minus the edit toolbar) by specifically disabling VisualEditor using both options in the settings (the "enable VE" one and the "disable VE while in beta" one).