If Putin visited Germany he would be surrounded by his own armed security. Any attempt to arrest him would lead to a standoff that would immediately end in him leaving the country or risk a military confrontation that would almost certainly lead to WWIII.
Imagine the German chancellor, or US president were captured by Russian police, even if they justified it through some international organization they helped setup.
The headline and article should read “Putin is unable to visit Germany without making a geo political disaster.”
Unfortunately heads of nuclear states, and their inner circles, are truly above the law. The only way to enforce it, is to risk escalation.