PII includes any information that can be used to link or correlate personal information. That includes usernames and account IDs. Every like/upvote contains that information, as well as a timestamp, indicating a unique account but also behaviour. The system doesn't just share a list of names, it shares a list of names with a lot of context. Stuff like this is also why pseudonymisation isn't sufficient to avoid GDPR obligations.
Usernames aren't sensitive information, so you can handle it without too much special care (although you do need to ensure basic protection of login credentials against data leaks, for instance by encrypting databases as a minimum requirement). They are PII, though, which means you're obligated to take some level of care and ensure that the information can be corrected or redacted everywhere.
The GDPR simply wasn't written with something like the Fediverse in mind. My server knowing when your account upvoted what posts on a third server would be ridiculous if we're talking about Twitter and Facebook, but it's the core of vote counting on Lemmy.
Dit kan alleen maar de bedoeling zijn van de BBB. Ze zijn tegen het concept van veestapelvermindering, dus door zo veel mogelijk onzekerheid en spanning te creëren rond de plannen die we al hadden, wordt het bestaande werk van politici die wel iets nuttigs willen doen langzaam ongedaan gemaakt. Met een beetje geluk worden de boeren er boos van, kunnen ze weer lekker wegen blokkeren, dat heeft de BBB eerder ook al aan de macht geholpen!