I primarily use Lightroom Classic, but have many collections syncing with Lightroom on my iPad. On rare occasion, I'll import images from a card directly to Lighroom on the iPad. These then sync back to Lightroom Classic into a folder called "From Lr mobile." I would like to move these from this collection into my regular Classic folder and collection set structure. Can I just drag and drop, or does that break anything with the mobile version of Lightroom?
That is possible, however while you are doing that you need to pause the syncing in Lightroom Classic or a copy of the original file in storage in Adobe Creative Cloud will immediately sync to Classic. Once the originals are in your folder structure you can add them to collections in Classic and have them set to sync. Use your iPad to delete the originals from the cloud, at this stage you can reactive sync in Classic so that smart previews will be available to your mobile devices.
pretty sure you don't need to pause sync and Classic will just follow the file in the new location and keep syncing it. I've never paused syncing and drag synced files around all the time. No new copy gets downloaded. Another thing to do is to change the syncing location in Classic's preferences and just set it to the exact hierarchy that you use in classic such as the dated folder structure. Your files (newly) synced from the cloud will just neatly file into the same folders you already use and be synced from there. If you ever want to delete them from the cloud, delete them on the iPad or simply unsync them in Classic (remove them from the all synced photographs special collection) . They will remain in Classic but be deleted from the cloud.