They're not being targeted for terrorist activity per se; they're being targeted for providing material assistance to terrorists.

Per the Treasury Department:

"The Autistici Inventati is an Italy-based far-left organization that provides a range of technological tools and services to violent left-wing extremist groups, including website hosting on foreign servers, encrypted email accounts, chat and video conferencing, and digital architecture associated with its “Noblogs” platform. Autistici Inventati identifies itself as an “anti-fascist” and “anti-militarist” organization opposed to capitalism and exclusively provides its services to vetted individuals, collectives, and groups it perceives to be aligned with its ideology, including to sanctioned terrorist organizations such as the Kurdistan Workers’ Party (PKK), which has been designated by the United States, United Kingdom, and European Union for its use of terrorist tactics leading to thousands of deaths in Türkiye, Iraq, and Syria since its establishment in 1984.

"Autistici Inventati is being designated pursuant to E.O. 13224, as amended, for having materially assisted, sponsored, or provided financial, material, or technological support for, or goods and services to or in support of, an act of terrorism." https://home.treasury.gov/news/press-releases/sb0616/

Per the State Department: "The A/I Collective provides encrypted tools and services to numerous violent far-left extremist groups operating in the United States and around the world. Many of these groups have relied on the A/I Collective’s digital infrastructure to plot or incite violent attacks, recruit others to engage in criminal activity, publish official communiqués by U.S.-designated foreign terrorist organizations, and disseminate maps of critical infrastructure, along with instructions for building improvised explosive and incendiary devices – all routed through a network of foreign servers intended to conceal criminal activity from law enforcement." They then go on to list the specifics. (https://www.state.gov/releases/office-of-the-spokesperson/20...)