In Germany it is not so easy. Even though the requirement for the state to get info about somebody's bank account is lowered, they still need some justification.
>I would have thought the reason for the raid was to collect physical evidence
For that reason alone the police wouldn't have to seize this 3d printed model of a nuclear bomb. Police stated, that „they might be planning a bomb attack“. This raid was also a display of power, to intimidate.
>why it's a problem that your account data would be in the hands of the police?
All people who donated are now on a list in some police department, maybe called „Connected to left extremism“. As donating is not a crime (both Zwiebelfreunde and RiseUp are registered organizations in their countries), this will not lead to prosecution alone.
But just because it wasn't illegal does not mean the police won't investigate if they feel like it.
And whenever they want to target you (even if the reason is unrelated), they can look up their lists and tell the judge: „Well, person X donated to this suspicous looking site, makes him suspicious, right?“ This might play a role in court or for new justifications (f.e. the police wants to raid your home, too).
[0] https://www.thueringen24.de/img/incoming/crop214771927/17338...