Many countries still don’t need a visa, you just fill out your itinerary ahead of time online and pay ~$20 USD equivalent fee(thanks to e0qdk for the conversion).
Instead of filling out a visit registration card after arrival, you fill out your visit registration ahead of time online.
Streamlines entry, boosts security.
Alright, Europe Direct has answered:
“You will not need an ETIAS travel authorisation if you only remain in the international transit area of a Schengen airport. However, you must have a valid travel authorisation if you leave this area and enter the territory of any of the European countries requiring ETIAS.”
So if your layover keeps you in the transit area of a Schengen airport, you don’t have to register with ETIAS, but if you have to exit the transit area, cross border patrol and check in again, which does happen sometimes with separately booked flights, you will have to register with ETIAS.
That is how every country I’ve ever been to does transit.
If you go through border control, you have to register, but if you don’t then you don’t.