Here is mine. 13” Nano texture. Still under 14 day return period. Build month is May. At normal distance I really cannot see any grain, only when I take a photo with macro setting on my Pixel 8 Pro phone. I have a feeling all the 2024 iPad 13” will have this issue, some more some less but not perfect. Even the 11” OLED. At this time it will be a waste of time to exchange it hoping for a perfect display until Apple officially addresses the issue and fixes it in the next batch which who knows when that will be.
Thank you for your data point, that is exactly what my eyes see when looking from around 20-30cm.
I have investigated slowly over time and was digging up Samsung S24 Ultra reddit threads that talks about this grain issue.
Interestingly a Samsung employee openly talks about this issue (not officially of course). And he/she accumulatively looked through multiple units across various production batches, including other models like S23U and Flips. He/she said that some units show this symptom more while some is minimal, and that later production batches show lesser symptoms than the earlier batches. The different datapoints are scattered in multiple threads and comments by this guy/gal.
https://www.reddit.com/r/GalaxyS24Ultra/comments/1ahcihd
I mention this because Apple uses Samsung (and LG) as the panel supplier and they both exhibit the same symptoms.
So I have some hope that this issue can become smaller the later the production batches for these iPads. However, like what you said, the best hope is to wait for the next major iteration, the M5 iPad Pro.
I will try again in the next month (or few months). I will try again for 1 or 2 times to see if the issue is minimized enough that I can live with it.