I'm willing to give this the benefit of the doubt if there's a lack of english-language reporting, and I don't want to trivialize as it's tragic wherever it occurs, but
- Wikipedia[1] has six events dating back to 1983 plus one from 1913, with a total of 46 deaths.
- CNN[2] only covers 2009-2018, with one German school shooting (to 288 American)
- Infoplease[3] lists mass shootings (not just schools) worldwide from '96 to 2021, with four German shootings and 36 deaths.
At 4x the population of Germany, the US (again, Wikipedia[4]) passed 180 deaths counting from Jan 2000 to June 2014 across 65 fatal shootings (there's many more with just injuries).
Looking at just "mass" incidents (5+ deaths) to filter out all the 1-2 casualty isolated incidents in the US that get overreported, those two wikipedia sources list two German shootings with 17 and 16 deaths since 2000 compared to the US with thirteen: 10, 6, 33, 6, 7, 27, 6, 5, 10, 6, 17, 10, 22, which is a ratio over 1:5. The math for your claim does add up per capita for just the decade 2000-2009 (both German @ 33, first four US @ 55).
[1] https://en.wikipedia.org/wiki/Category:School_shootings_in_G...
[2] https://www.cnn.com/2018/05/21/us/school-shooting-us-versus-...
[3] https://www.infoplease.com/us/crime/timeline-of-worldwide-sc...
[4] https://en.wikipedia.org/wiki/List_of_school_shootings_in_th...