Anyone who supports Putin's terrorist regime should be investigated to see if they provide material support to terrorists.
Supporting war crimes and ethnic cleansing is not exactly kosher in Germany, so they might get arrested.
German citizens can protest as long as they don't break any laws in Germany. I am not sure if support for the Soviet Union or Communism is
allowed in Germany. In the former Communist Eastern European countries, they would arrest your ass in a New York minute.
Does it make sense morally to support Russia's terrorist activities in Ukraine? Of course not.
In Latvia, I would also face up to five years in prison for openly supporting the operation in Ukraine. Convincing victory of democracy over freedom of speech, it's good that I'm not in Latvia.

State terrorism is illegal in most civilized countries. Why are you surprised?
Why do you live in Latvia? Go back to your beloved Russia.