Are you just saying they're not as bright or is there something more there?

On OLEDs, high levels of ambient light hitting the monitor tends to wash out blacks, making them appear dark gray, thereby subverting one of the most clear-cut advantages of OLED.

I don't see this on any of my phones or wearables. I'm aware QD-OLED in particular has this weakness, but haven't heard of or experienced any other OLEDs having this issue.

I wonder if it's actually due to the quantum dots, or if it's more broadly a thing for large OLED panels. I haven't spent any significant time using an OLED TV, and I think most of the OLED computer monitors I've seen in person were QD-OLED.

The story I'm aware of is that in the QD-OLED display stack it was not possible to put a polarizer layer in, which is what causes its telltale weakness in ambient light rejection.

So you'd also not see this on other types of displays with a quantum enhancement film (i.e. FALD MiniLED + quantum dots), it's specifically QD-OLED that has this weakness.

This is to the extent that if the self-emissive quantum dot demo from this year's CES was real, even that won't have this issue (although it will likely still do have the stupid triangular subpixel geometry like on QD-OLED, as the demo unit also had that).

TFTCentral did some pretty extensive testing on this topic: https://tftcentral.co.uk/articles/the-oled-black-depth-lie-w...

I guess I see this in bright, direct sunlight on Samsung Galaxy phones but its really not an issue, especially for a monitor.

And it's not an issue for other display technologies? Why not? Do the OLED cells have high reflectivity or something?

I don't know the mechanism behind it, but I've done side by side comparisons and it's clear to the untrained eye that the impressive contrast ratio of OLEDs is easily weakened by ambient lighting conditions.