I see white specks on neck feathers as new feathers are growing in after a molt. Pictures can help us to determine if it is that or lice eggs. If there are lice eggs, you will see moving lice when you part the feathers. Most lice are located under the vent area while another type is found around the neck and under wings. Here is some info with pictures of lice and eggs:
https://the-chicken-chick.com/poultry-lice-and-mites-identification/
https://the-chicken-chick.com/poultry-lice-and-mites-identification/