A possible retaliation by the EU could be to not enforce US intellectual property rights in the EU anymore. Or we could start taxing cloud companies, who, until now, have not paid taxes in the EU for profits that they generate in the EU.
Like other comments said, this could work only if this was long term and everybody bites the bullet until they have a good local alternative to foreign offers with high tariffs. And the chances of having a lower offer as the one you were importing are really high. So, everybody is betting on short term.
The good thing is: If the EU finds a way to tax the money flowing from advertisers to big tech, consumers would not be affected (at least not financially), because they are not the ones paying the price.
You gonna tax their real customers, the advertisers. And a 100% tax on advertisement is actually healthy for the economy and society.
Those are free for consumers, but Google Suite (Mail, Calendar, etc.) for enterprises definitely has a price.
There are some things where I have my doubts about the current actions of the European countries, like rearmament. Will that be dropped the minute a new US administration enters? What the EU does well, like really well, is trade and bureaucracy. It is, in my mind one of the few areas where the EU can absolutely run circles around the US, while managing to protect and isolate itself from the worst fallout. We've already seen this with the current EU tariffs, they are extremely precise and targets Republican votes at almost no cost to EU consumers. I think that will continue, rather than imposing broad tariffs, the EU will target things Trump care about specifically.
A lot of the discussions happen during the informal after-hours in cafes and restaurants.
This is one of the reasons why, for many years, the Dutch delegation was very unsuccessful at pushing their own interests and placing their representatives in "important" positions, as they were all keen on taking the first train home from Brussels, and were skipping these informal gatherings.
It's not a stretch to imagine that a poor mastering of the "important" EU languages will put a politician at a disadvantage in such settings, due to an inability to communicate with his/her peers.
How do you plan to ignore IP to hurt American tech companies. I guess if you allow piracy of all of netflixs content that would work (but same thing would hurt spotify).
Most tech companies are not protected by IP but by network effects and vendor lock in. It would be far simpler to simply implement a minimum tax on revenue or advertising spend in country to extract value.
Make piracy legal for downloaders, and stop enforcing the criminal law for seeders.
Hence the retaliatory tariffs. The backdoor taxes through 'laws' (that are NEVER enforced against EU companies -- Spotify got a DMA carve-out).