Can't copy or move online-only files to my computer's Desktop

Hey PixmaStar - sorry to hear you're having issues with this.

From what I gather you must be using a web browser to do this - right? 

If  that's so, have you tried clearing your browser's cache and/or using another browser?

Keep us posted! 

Thank you for your reply!

I hasten to inform you that I use the application installed on the device through which I previously added files, and the application installed on the device through which I am trying to download

I see, so you're referring to the Dropbox desktop app or the Dropbox mobile application instead PixmaStar?

Can you send us a screenshot of the loading bar you mentioned to have a visual too? 

I use the app for macOS and windows

This is the app's usage on your computer PixmaStar - can you send us a screenshot of the Dropbox desktop app's exact status as shown in your system tray/menu bar?

Translation from Russian to English:

In the system tray: Updated
In the application: All files are updated

So everything seems to be fine on the Dropbox app and your files in the Dropbox folder should already be synced PixmaStar 

What is the exact issue that you're facing at the moment? 

(Windows) Now when I try to copy a folder with files (folder size 300-400 MB) there is no copying progress when copying. Copying progress is 0% and does not advance.

However, if I copy a folder on a MacOS device, copying occurs in 20-30 seconds

I probably found a problem. I have several folders in my account, but they have different status (there is a status with a green checkmark and there is a status with a cloud). When I try to copy a folder that has a status (green checkmark), then copying occurs without problems, but when I try to copy a folder with a status (cloud), copying does not occur.

Oh, I see now, thanks for the additional details and clarifications PixmaStar  

What you mention is actually expected when it comes to online-only files, as they'd need to be made available offline on your computer before they can be copied or moved to your computer's Desktop (or any other) folder. 

For more information on the syncing icons and their meanings, you can take a look at this Help Center article.