Aquila
You are definitely right about OS updates. In fact, we need to talk more about OS/software updates, as they can absolutely change whether a phone gives you eye strain.
The panel, driver IC and power rails are usually where the temporal artefacts/other strain related issuss come from, but vendor/iOS/Android updates and firmware decide how that hardware is driven. So an update can make a phone once tolerated for months suddenly become painful to use (or rarely, make a painful phone feel fine).
If eye strain starts right after an update, then software interaction is likely the prime suspect.
Vendor, iOS and Android updates can push display firmware or driver updates that change PWM frequency or duty cycle and enable/disable DC‑dimming, alter panel power‑rail timing and subpixel drive schemes in the display‑controller firmware, change compositor/frame scheduling and vsync/timing (which can cause microstutter or sudden full‑frame brightness events), adjust adaptive/variable refresh behaviour (VRR governors, switching thresholds or forced fixed‑rate modes), tweak colour‑management and tone‑mapping (True Tone/auto white point, Night Shift/blue‑light filters, gamut mapping, HDR→SDR remapping), including dithering algorithms and temporal noise shaping, add or change software overlays that modulate brightness (software PWM/emulation), reduce white point or implement “anti‑flicker” filters, and change ambient‑light sampling rates and auto‑brightness smoothing so luminance switches happen faster or slower. Any of those tweaks can change the exposure to temporal light modulation or make transitions more abrupt, and that’s enough to increase (or rarely reduce) strain for sensitive people.
Hardware is the source and software is the control. Software updates are a plausible and common cause of eye strain when display behaviour changes post‑update. Therefore this also becomes a risk with updating software on a once comfortable & usable phone, and we never know what display changes could take effect with the update.
I've been using android firewalls consistently to block/postpone software updates on the Realme 14x. I did the same for a while on the Realme 9 pro. However I slipped up with the Honor 70 Lite, and decided to update, which resulted in the phone becoming unstable and unusable.