We can add simple boolean Radio buttons as EAV attribute in install schema by this code:
"type" => "int",
"backend" => "",
"label" => "Test",
"input" => "boolean",
"source" => 'Magento\Eav\Model\Entity\Attribute\Source\Boolean',
"visible" => true,
"required" => true,
"default" => "",
"frontend" => "",
"unique" => false,
"note" => ""
But if we want to add more than two options or other than 'Yes'/'No' Type then how to achieve this. I guess this could be in source attribute but have no idea how return the options in custom file i.e. to which file extends or implements and which function need to be used. I am unable to find the answer anywhere else. Thanks