Thyroid disease cannot be spread through kissing or other contact.
Since Thyroid disease disorders are non-communicable diseases which means they cannot be spread from one person to another through kissing or through any other contact.
Also because Thyroid disease is not communicable it cannot be spread through sexual contact either so you're safe to have sexual intercourse with someone who does have Thyroid disease.
You won't and cannot catch Thyroid disease from someone who has it.
However if you do have Thyroid disease your sexual performance and sexual functions can decrease when you have the Thyroid issues.
But it cannot be spread through contact whether sexual or not.
You can safely kiss someone with Thyroid disease.