I am using Linux comfortably

I have found Linux to vary from Distro to Distro

Mint never worked well for me, but Lubuntu with XFCE was pretty decent

I've came across the Trinity Desktop Environment, which is a modern fork of KDE3. Could be worth trying given it's "older".

KM Can you describe the known-good VNC connection in more detail?

Markus The Android app is bVNC v5.0.3 (I haven't tested later versions). The VNC server on the Linux computer is TigerVNC. I hope I'm not missing something - it's been a while since I've used it. I'm not confident it would work for other TV devices, too. There might be other factors at play. One of it may be that Android itself is comfortable to use on the device in the first place.

KM Thanks a lot. What vnc tool/which version are using from your known-good desktop to connect to another desktop that is not save for you? I.e. which setup do you use to access ledstrain?

KM 30 Hz does contribute to the strain, but not significantly.

KM can you tell us more to the other hardware of you desktop, CPU type and generation? What means compositing disabled, how to enable that? Does current browser usage with Debain 11 cause more strain?

Markus It's a very old system: Dell OptiPlex 755, Core2 Duo E7300 @ 2.66 GHz. Disabling compositing for Xfce means going to "Applications - Settings - Window Manager Tweaks - Compositor" and to uncheck "Enable display compositing". I use the Firefox browser, which has the version 102.6.0esr. By default, it does not use hardware acceleration unless it is explicitly enabled in about:config. I don't think the default settings cause additional eye strain.
I also disabled font anti-aliasing and installed the Microsoft TrueType core fonts (known from Windows XP), which unlike other fonts still look good when anti-aliasing is disabled. A downside is those fonts haven't been updated in years, missing modern Unicode characters (like the search icon in this forum's search bar for example). Disabling anti-aliasing may or may not have an impact, I'm not sure about that yet.

KM can you tell me the full name of the MSI GT710 card. The don't know which name match to the first generation. I will give you setup a try. Thanks a lot for your detailed information.

Markus MSI Nvidia Geforce GT 710 1GB DDR3 PCI-E 2.0 HDMI + DL-DVI-D.
I know there's a later generation of this card. I'm not sure how to distinguish them.

KM Try the Bitstream Vera fonts too, I like the mono one in particular. They're also fully hinted and from the same era. https://download.gnome.org/sources/ttf-bitstream-vera/1.10/

I'm looking for other options as Windows 2015 LTSB isn't cutting it for me. Anyone recommend a comfortable distro I should try?

bz12 Pop OS comes to mind.

EyeDiscomfortCertificate just tried and it was uncomfortable for me.

bz12 Oh, you mean visually uncomfortable? Yes, font renedering is worst on Ubuntu based distros. The most likable font renderer for my taste are on OpenSUSE and Manjaro.

KM Disabling anti-aliasing was definitely the key to solving my eyestrain problems on all the operating systems I use (Windows, Ubuntu, Android). It took me months of searching and looking down many blind alleys before I discovered that anti-aliasing was the cause of my problem (Why is this so hard? Why is there so little discussion of this as a cause of eystrain in mainstream media?) Months more research to find reliable, comprehensive ways to disable it but once I did - bliss. I can now use my devices for as long I want with zero eyestrain.

George357 I'd be interested in trying this if you have any sources to share for guidance.