The conspiracy nuts muddy the waters concerning feed; there's a much simpler explanation for the phenomena reported, especially when it is experienced keepers making the report. See, e.g.The logistics of purposely adding chemicals to enough feed to have any impact on the laying in backyard chickens that would even register as a percaentage in loss of egg sales for the major egg producers make the idea impracticable.
It also doesn't make much economic sense given the scales involved.
A reduction in feed quality may impact a hens yearly production but hens still lay eggs with sub par nutrition as I've seen at the allotments.
https://www.backyardchickens.com/threads/feed-date-code-translation.1249955/post-20055764