It looks like there is no lineage code available for the Doogee N20 (originally with stock Android 9.0, upgradeable to Android 10.0). Thus, the chances of a /e/OS custom ROM are more than slim. However, a /e/ GSI-Q V1.4 can be installed.
First, an unlock code has to be generated to unlock the bootloader.
With fastboot oem unlock ****************" (replace * with 16 digit unlock code) the unlock process is initiated.
Check if bootloader is unlocked using the below commands fastboot oem get-bootinfo
The next step could be as described in the /e/ documentation:
How to /e/OS on a non supported device?