I have been doing the therapy for almost a year now -- and have some progress but not as much as I had hoped. With the pandemic, I am not seeing my specialist.
The good news is, I have found/gotten used to a decent setup.
I can use the HP EliteBook 840 G6 for many hours (8+) with almost no pain or discomfort. It is running Windows 1809 (Build 17764) -- Windows 10 Enterprise. It is a company issued laptop and I don't use Flux. I attach it to a HP 23er 1080p monitor and a BenQ GW2765HT 27 inch 1440 monitor. In this manner I have 3 screens...the "best" is HP 23er. However, I use all of them for the 8+ hours.
For personal use, I have a Thinkpad T430s. Interestingly, it got worse for me as I got more used to the EliteBook, but is still usable for hours, with some minor discomfort. It is running Windows 10. I in general prefer Linux, but the fonts rendering seems to be much better on Windows (I guess ClearType), so I switched.
For smartphone, the best I have found is the LG G7 (currently Android 9, Kernel 4.9.112, on June 1 2020 patch level). When using it for long periods of time (like 5+ hours on a flight) I do get headaches. It initially did give me mild headaches and eyestrain. Now, I use it for 1 hour at a time, with some break, and get little to no discomfort.
The setup I have here is relatively "modern" but I know it will not last forever; so I will continue my therapy and looking for new devices.
Unfortunately the therapy is not perfect -- Macbooks and Dell XPS 13 still give me dizziness and headaches. I hope with more therapy, these will become usable.