I see no problem building it. Sources you can find here if it is the same as A6+ https://forum.xda-developers.com/galaxy-a6/development/rom-lineageos-16-0-galaxy-a6-plus-t4019619
EDIT: The device seems to be treble supporting. Than you can try the eOS PIE-GSI. Example/HowTo here [HOWTO] install eOS GSI on a Treble device - new GSI added June 14th