itch.io

Honestly, that's a good question, but I (and a number of other users with issues) don't know. I'm not normally affected by anything on computers in this way, so the usual obvious triggers (of which there are at least half a dozen which have been clearly identified and reported by users for whom they're known to be problematic) probably aren't the ones affecting me, or at least aren't individually causing problems. Even without having seen some of the responses from staff, the best case scenario would be willful ignorance. And there have been direct statements from both support staff (third party) and Valve employees, not just saying that they have no current plans to address the issues, but that they are aware of the problems and are knowingly choosing to do nothing to solve them. They've done plenty worse than this too, but this isn't really the place to go into the scale and severity of abusive conduct I've seen there.

For a bit of context, though, this is a quick mention of the first few issues that come to mind which have been clearly identified as being active triggers for multiple medical conditions:
-excessively high contrast colours in some areas of the UI, exacerbated by changes in how game cover art/thumbnails are displayed.
-glitchy flickering on multiple screens in the app on some devices (not dependent on system specs, sometimes higher end PCs have issues and lower spec systems don't, and vice versa).
-flickering effects caused by multiple instances of loading images on almost every page in the app which has images.

That last one is noteworthy because if the update which caused all these issues hadn't included the removal of several features for modding the app, about 80% of the problem was in areas which mods could have fixed, but because of other parts of the update, the necessary tools no longer exist so the issue is 100% unfixable without excessive use of third-party tools. The colour contrast issues can be worked around fairly safely with graysale mode, but that causes issues of its own (and can be service-breaking in some instances), but most of the other options have unstable or unreliable workarounds at best. And, as mentioned, there are several more clearly identified issues, as well as potentially some problems caused by interactions between the known problems, or by something else going on with the app that's not as easily identified.