Putting this piece of info here follow up a call that DS and Elliott had with Adyen since it is impactful to our consideration on which upgrade approach to take:

Since we last spoke, we did some researching on our end and found documentation from the Security Standards Council explaining how iFrames is PCI compliant and only requires a SAQ-A. I have also confirmed internally that the Drop-in integration only requires a SAQ-A to be provided annually to Adyen. (PCI Standards Link)

Adyen came back to explain that Pay-by- Link won't work for us so the Drop in solution would be the way to go if we upgrade:
Hey Evelyn,

After discussing Wikimedia’s integration with our product team, I’m sorry to say we aren’t able to offer Pay By Link as a direct HPP replacement to Wikimedia. Our checkout team has positioned PbL as an integration add-on intended to fulfill specific use cases like email or chat messaging. Adyen feels confident that a native Drop-In solution will fit merchants' checkout flows better than a hosted PbL can while providing a better overall experience.

To give you a little more background behind the scenes at Adyen, Pay By Link is a much more resource intensive payment option which requires us to maintain and track the state of the payment link (as opposed to our components which are stateless). Because of our confidence in our Drop-In solution in place of HPP, PbL hasn’t been scaled to handle the type of volume Wikimedia would throw at it.

I know we talked a good deal about PbL on our call, so I am of course happy to answer any more questions you might have about our Drop-In solution as well. I also double checked with our compliance team who assured us that based on Adyen’s risk appetite, the SAQ A has been assessed as the most suitable documentation for our encrypted solutions (checkout) as all the credit card activities are outsourced to us. If your auditor has any more PCI related questions, we are happy to address those as well.

I am very sorry for the miscommunication on this issue initially!

Best,
Tyler