"Google AI said: "Decaf can decrease the absorption of specific medications and supplements—including thyroid medication (levothyroxine), iron supplements, and some antidepressants—if consumed simultaneously.""
— @Catina
GoogleAI says that decaf can decrease absorption and then throws everything into the same bucket. It's best to sort out everything once it does that. Coffee, including decaf, is well-known for decreasing absorption of Levothyroxin. So since your taking that, it makes sense to be extra cautious with decaf, too. But timing matters, too. Those on Levothryroxin can drink coffee after an hour or so of taking their med, giving it enough time to be absorbed. That's what I did when I took Iron supplements and couldn't drink milk or take an antacid until 2 hours elapsed. As for absorption of other meds, like some antidepressants (including SSRIs), any absorption effect is basically nil. Worrying about it is likely to cause more "harm" than actually taking them together.
Now, caffeine is more apt to be an issue, but that's for those who are sensitive to it or consume a lot of it. But caffeine by itself has really no effect on absorption.
So yeah, it's good to know about decaf and its potential effects, but it also helps to know where more caution makes sense.👍