Milk thistle (and extracts) have long been recommended, uncritically, for those with thyroid issues, especially if they seem to have liver problems.
This new article is long and detailed - and questions its safety and the effects it might have.
Milk thistle alters thyroid hormone transport
By thyroidpatientsca on January 16, 2022
I'll not try to summarise - much better to go and read the article.