@David_J-42.ww 

Hello David.

I use the VR2100, one model down from the 2800 you're using. Nevertheless, I think the options will be similar. Prior to your post, I hadn't looked into this aspect of the router offerings. I'm going to try to answer your question on technical and security levels.

Security
--------
The implementation on the router is extremely basic, and, in my opinion, not implemented well. I'm sorry TP-Link, but defaulting to the admin account for sharing is not best practice and does not promote a 'secure' posture to customers. Seperate account creation must be mandatory.

I do not advise this function be used to store or share any private or financial documents.

If you haven't change the admin account's password away from the default, please change it now, using a password generator such as https://bitwarden.com/password-generator/ . Please stick to the default 14 character suggestion. An 8 character password can be broken in 3 hrs. Check yours against https://bitwarden.com/password-strength/ .

Ultimately, if you need to share information, deploy a network attached storage device (NAS), that is properly suited to the task at hand.  There are other options available (Google, OneDrive etc...) but they require all users to be registered on said service.

Technically
-----------
I'm assuming that the router operating system used is Linux / UNIX based. This uses a series of permissions based around owner/group/others. Being prompted to access the device should then map the permissions correctly, for the computer you're using. If the default admin account is used, then this removes any permissions issues that may arise, as that account is 'God' on the router. However, there are also permissions within Windows which need to be considered.

1) If not already done, change your admin password as mentioned in the preceding section.
2) On the router, switch to advanced menus, then click on 'USB Sharing' -> 'USB Sharing
   Device' and create a new account. Set that account for use (should be automatically done
   when created).
3) Under 'Folder Sharing', ensure that 'Share All' & 'Enable Authentication' are turned on.
   This is the problem with the implementation; turning 'share all' on, negates permissions.
4) If both options on point 3 are set, try turning off 'Enable Authentication'. If this works,
   I would advise you stop using this function. This means unauthenticated access is in use.
5) If point 4 works, report this as a bug to TP-Link staff. Otherwise continue.
6) As already mentioned, the problem can also be within Windows 10 itself. Use this article
   to help you determine if the permissions Windows has set when you're browsing to the
   location are correct. https://www.windowscentral.com/how-take-ownership-files-and-folders-windows-10
   
There are multiple points of failure within the scenario that you're dealing with. I hope you manage to sort out the problem, but, I would recommend you look at implementing a proper solution that has data integrity and data safety at its heart; network attached storage device (NAS).

Kind regards,
Mike