not entirely sure what's going on, like you can still do the code but now it's color-highlighted and there's a slight loading-bar delay which kind of slows down editing, is there an option to switch that on and off for those with slower comps?
This is the closest thing we have to documentation for the new editor. It is a slight variation on the default editor for MediaWiki 1.33 so there may be more details on the general MediaWiki site. In short, it is just VisualEditor. It has a source mode but there is no separate source editor.
Coupling a basic editing mode with a buggy (historically speaking) visual editor has certainly caused discomfort for a lot of power users; at least the ones here on Community Central. Unfortunately, it seems we don't have a choice in the matter.
As for the text coloring, I assume that is analogous to the legacy platform's syntax highlighting. It is possible you aren't familiar with it if you keep it disabled like I do. Currently, there does not appear to be an option to disable it. I asked in the updates thread if such an option will be added and I have yet to receive a reply.