Great question — answering as the UphillTech team:
No. From the EU ETIAS website ETIAS travel authorisation is an entry requirement for visa-exempt nationals to enter 30 European countries for a short stay . (Emphasis added). If you are transiting airside you do not clear Immigration, so you do not need to meet the entry requirements for a short stay. The Exemptions and specific cases section of the FAQs on the above website addresses the question more explicitly. Do I need an ETIAS travel authorisation if I am only transiting through a European airport? No, you do not need an ETIAS travel authorisation if you only remain in the international transit area. However, you must have a valid travel authorisation if you leave this area and enter...
Full answer by Traveller: https://travel.stackexchange.com/a/204050 (CC BY-SA 4.0).
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