I don't see in the study linked in the article where it attributes light mode to more eye strain.
I found where blue light causes eye strain, and it most certainly does, I immediately notice the difference when using a blue light filter on my monitor, but you can have both dark mode and a blue light filter enabled.
You measured the dryness/redness of your/your partner's eyes after trying dark and light mode? Or is it just that occasionally you or your partner get dry/red eyes and the most memorable association was using light mode beforehand (and it's memorable because you don't like the aesthetics of it)?
I don't think this is "rocket science" but that doesn't mean it is handwavingly obvious either
I found where blue light causes eye strain, and it most certainly does, I immediately notice the difference when using a blue light filter on my monitor, but you can have both dark mode and a blue light filter enabled.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6020759/
Anecdotally, dark mode causes my eyes and my partner's eyes less strain.
You can notice by how dry and red they get, as well as the headaches, it's not rocket science.
EDIT (reached my post limit)
@shawnz: No, the light physically hurts. It's immediate. It's not because of the aesthetics.