These files are the smart previews of the data synced from the cloud on your computer. If you choose to sync data from cloud to your computer, this folder will be created. Please refer this similar discussion mobile downloads.lrdata and let us know if that helps.
Thanks for the reply, but
a) these are not smart previews, they are full copies of the files which I've downloaded, around 9Mb in size, and
b) I have looked at the discussion re mobile_downloads.irdata, and these files do not show up in the related download locations, possibly because I have deleted them from the "All synched data" catalog.
Surely when I delete files from "All synched data" they should also be physically removed from the "Mobile downloads" folder as well as from the catalog entry?
These are indeed originals, not smart previews. This file contains the images that were shot on your iPhone, for example, and then synced to Lightroom Classic. The easiest way to deal with this is as follows:
1: In your folder panel, look for a 'device' (like a separate hard disk) with the name of your phone or tablet.
2: Select all images on this device, and move them to a normal folder by dragging and dropping.
3: In Lightroom Preferences - Lightroom Sync, check 'Specify location for Lightroom CC's ecosystem images' and then click 'Choose' to select a normal folder for images downloaded from Lightroom CC.
4: Now you can manually delete the 'Mobile Downloads.lrdata' file.
Johan, thanks for that but a couple of points. The files no longer show under my 'device' after I have deleted them from the "all synched data" folder, nor are they saved in the cloud. As I already save the files in other folder(s), I will manually delete them from the 'Mobile Downloads' folder, I just hoped that Lightroom would save me the bother by deleting them when I delete them from synched data.
I'll mark this correct, no need to respond further.