I moved AdGuard and all subfolders and files the lot, one folder is just backup but I left it on the usb because there’s plenty of room.
So A folder called AdGuard is on the usb the same as it is when it was in /etc, mirrored, then I delete everything in /etc /AdGuard apart from the symbolic link.
Sometimes you put:

ln -s /mnt/usb_drv/AdGuardHome/AdGuardHome ./AdGuardHome
ln -s /mnt/usb_drv/AdGuardHome ./AdGuardHome
Which is it, thanks