Android 10: Device Admin Enrollment Deprecated
Problem
Section titled “Problem”Android 10 devices cannot be enrolled as a device admin. This means that Samsung devices cannot be enrolled as “Legacy - Device Admin” from the Samsung KNOX portal.
If you try to enroll a Samsung Android 10 device, the enrollment will halt when you try to activate the KNOX License.
Google has deprecated Device Admin in Android 10 due to security issues.
Source: https://www.android.com/android-10/
Scroll down to the Enterprise section

Solution
Section titled “Solution”In order to enroll a Samsung device, you will have to enroll as a Device Owner instead.
Create a new MDM profile in Samsung KNOX portal: Samsung KNOX Mobile Enrollment (KME)