Recently I upgraded to Lightroom Classic 12.0.1, and also set many of my photos stored on my NAS to "on demand sync". I do not have any cloud-based images in my Lightroom catalogue. Since then, when I run Lightroom Classic, periodically a box appears saying "Lightroom is downloading from Pictures", plus "Learn more in Settings->Automatic file downloads".I am unable to find that item anywhere in "Preferences" or "Catalog settings"; does anyone know where it is, please?
For files that aren't stored on the PC, I don't want them to be requested from the NAS until I edit them, because that was the whole point in using "on demand sync" in the first place, and indeed I haven't seen any evidence that any are being stored locally as a result of these downloads - which begs the question of what is being downloaded and where is it being stored?
This is an interesting setup & it might not function with Lightroom Classic as you expected.
Lightroom Classic does not store images within itself; it creates a link to the original pictures & by design, it tries to reach the original image.
The popup you're referring to might also not be generated by Lightroom Classic. The NAS management software must be notifiying you about Lightroom Classic accessing the images & the way you've set up things, and it could mean 'Downloading' for the 3rd party program.
You can try two of these suggestions & share the outcome with us here.
Import some images from the internal/local storage in a new & empty Lightroom Classic Catalog from File > New catalog.
2. Try generating smart previews for the images on the NAS & ensure 'Automatically write changes into XMP' is disabled from Edit > Catalog Settings > Metadata.
You're right that the popup wasn't from Lightroom; it was from Windows. It seems that the problem happens in library view when I hover the mouse over a library subfolder, and this causes Lightroom to download the first image in that folder which it then displays at the top left of the screen. If there was a way of making it get the image to show there from the previews, or indeed not show it at all in library view (since knowing what was the first photo I took on a particular day isn't much use for anything), I think that would fix the issue. Not having the library folders expanded also seems to help, but this isn't always possible.