it has digital license and shipped with Ubuntu i didn't use it  then i install wind10 and delete Ubuntu but it give me the error above

Systems shipped with Windows 10 from Dell do not require user activation -- contact your seller to find out why your system won't activate.

If it shipped with Ubuntu, it does not have an entitlement for Windows 10.  You will need to purchase a license key for a full version of Windows 10.

i bought another lap from two months ago  , and it has also Ubuntu but i delete it then install windows and it activated automatically by digital license ?

Unknown, unless the system originally shipped with a Windows license.  Generally, Dell systems that ship with Ubuntu do not.

It's clear from your earlier post that the current one doesn't have an entitlement - so if you want to run Windows on it, you will need to purchase a license.