While filling the booking form on Kiwi.com, I noticed that below the passport/ID expiration date there is a box "No expiration" that can be checked.
See screenshot here:
This made me wonder: Does any passport never expire?
There are quite a few national ID cards that don't expire in some cases :
Frame challenge: The point is not that the document never expires, it's just it does not have expiration date printed on it anywhere, so it is not a part of document data.
Obvious examples: Russian domestic passports do need to be replaced when you turn 18 and 45 years old, but that date is not printed anywhere in the passport and is flexible (expired passport is still valid and needs to be replaced after the fact).
Russian birth certificates never expire, but they stop being IDs when you come of age. However, that date is never printed in the document. As soon as the kid gets their domestic passport they stop using birth certificate as an ID.
These are primary documents on which Russian citizens fly domestically and they are specified with no expiry date.