I further removed the CharInsert gadget and, just to clarify or reiterate, have disabled Reference Previews globally and locally. I have Navigation Popups enabled, but also disabled the ReferenceTooltips gadget.

I tried editing any page on English Wikibooks and Meta Wiki and the 2017 wikitext editor component of VisualEditor loaded up normally. It works normally on non-Wikimedia wikis.

One thing I notice is on English Wikipedia, there is an option in Special:GlobalPreferences that says "Temporarily disable the visual editor while it is in beta." That doesn't appear on any other Wikimedia wiki. That is, if I try setting my global preferences from another wiki, there's no option to set. So, that could be the problem, perhaps.

Okay, it looks like when I was updating my global preferences from within English Wikipedia, I was enabling some preferences that can be set globally and must've accidentally enabled that English Wikipedia-only "Temporarily disable the visual editor while it is in beta" option (when I meant to untick the second box). In my troubleshooting, I set a local exception by unticking that second box, and it wouldn't let me untick it (since it had been set globally, I guess). When I went back in to Special:GlobalPreferences, I was able to unselect that option, then unselect the local exception in Special:Preferences. It's not very clear, so perhaps the wording of the first and second checkboxes next to each preference item could be clearer in a future release. Nevertheless, doing that restored my ability to use the new wikitext editor.

In T256519#6261225, @dmehus wrote:

I was able to unselect that option, then unselect the local exception in Special:Preferences. It's not very clear, so perhaps the wording of the first and second checkboxes next to each preference item could be clearer in a future release. Nevertheless, doing that restored my ability to use the new wikitext editor.

@dmehus thank you for documenting the steps along this journey in a way that makes it easy for us to follow along. I'm glad to hear you have access to VE again, albeit by way of having to navigate a series of preferences.