That's a helpful timeline.
The "feature parity across these clients"* part should include a disclaimer, *except for dark color theme feature parity, of course ; )*
How did MacOS, iOS, and Android color theme feature parity jump to the front of the line on those priorities and leave Windows at the back or as the designated driver?
What other clients are there than the two main desktop, Mac & Windows, and two main mobile, Android & iOS?
Is it likely that if the development team used Windows instead of MacOS then it would have be prioritized or at least been included?
Aside from the number of details of the matter discussed above for the technical issues, if Dark Mode were a priority, would it not also be pushed out just like any other priority or feature parity?
Perhaps, it could be less of a timeline and more of a dev-user, competitive, or business preference, but then don't devs and ceos also use the customizable Windows, and doesn't EN have to also compete with all the other Note-taking cross-platform apps that have already included the Mac, Android, and iOS clients in their Dark Mode feature parity?
...but all that is only speculation based on experience of what's been delivered.