Sorry, my explanation for precisely what I was dismissing was in the first paragraph of the previous post (and the entirety of my first response). I was referring to how I thought you were saying the thing that need to be fixed is that Dark Mode should have a light editor instead of dark. 
Your initial description was:
“In the latest beta, when I select dark mode, the page background becomes dark, instead of staying white as in MacOS. This makes the text difficult to read and dark mode unusable here.”
And in follow-up:
“…In Mac OS, Dark Mode behaves the way I want it to by default, i.e. the interface is dark but the page remains black on white.”
Which to my mind says nothing about the very specific rendering flaws in the tutorial, and is saying that the fact that we don’t have a light mode editor in dark mode is the flaw, a phrasing I would still object to.
So it probably doesn’t help that when I responded there were only four screenshots up, and the entirety of your report was focussed on whether the editor should be light by default.
Did you try, as suggested, using a fresh copy of the tutorial from the Mac? You should see most of these issues in the beta copy of the tutorial are indeed wonky formatting within it. I don’t believe it is even possible to reproduce these problems today, but once again if you can, please let us know how.
We could create code specifically to make the broken beta tutorial from 2017 look nice, but I think it’s better to just fix the tutorial. It’s an example of something no word processor should ever create. This one did—early in its alpha phases before the beta was even released—but as far as I can tell it no longer does.
The main outstanding issue between the two (other than the colour treatment algorithms) is the one that I addressed at length, and that is how the Mac RTF generator uses cf0 to indicate no-color text, which the QT RTF parser reads as black text—which is why when you remove the colour on the Mac it stays black, because (to reiterate) the way it removes colour is the way the PC version sets black. I do believe that is something we can solve, and should, but it is also something very easily self-corrected with the Documents ▸ Convert ▸ Text to Default Formatting on the PC, for the time being.
Hopefully with that tip in mind, and the Alt,d,c,d menu accelerator in mind, you can nuke the problem at the binder level before getting into even looking at the project. It’s so easy to do, that it doesn’t really matter if your workflow is one-way and doesn’t involve bringing Windows modifications back to the Mac—in fact that’s something I routinely do when switching platforms anyway, because of the myriad font differences and so forth—the font I prefer on the Mac looks awful on Windows in general for some reason (Type 1 PostScript OTF turns into pea soup in my experience). It most certainly is a workaround for this specific problem however. As I’ve said several times now (first in a glossing over of how all of this is WIP), we need to fix that, but I’m not sure where it is in the stack of priorities.
Everything gets logged as an issue. You wouldn’t believe the minutiae that I file every day. Yesterday I logged how you can’t right-click in the inspector keywords listing area to more conveniently bring up the same menu you get when clicking on the ••• button specifically, not but centimetres above it. This is a convenience we’ve built into the Mac version, but it is missing on the Windows version. It’s ultimately trivial, and there are dozens of things they should be spending their time on rather than that (such as auto-completion of existing keywords in that same area when typing)—but it is logged, and will remain logged until it is fixed, and I can remove the styling that deletes the passage from the Windows user manual that refers to right-clicking.
Today I filed that Edit ▸ Find ▸ Use Selection for Find should also propagate the selected text string into the Edit ▸ Find ▸ Project Replace tool. I doubt anyone is foaming at the mouth over how that doesn’t currently happen, but it is logged, and will stay that way until fixed.
The black text bug is logged. With every beta release, it is looked at again as I can see from the milestone reporting. It is not forgotten; it is problematic.
Yeah, I don’t know what is going on there. Guess what else is logged? 