Permissively licensed open source code is open source code. Firmware on a secure element can be open source without it being possible to replace it without the signing key on a production device.
German courts are not bound by precedent in the same way as US courts and you're referring to a specific case in Germany which cannot be broadly applied.
AOSP ships a lot of GPLv2 code (Linux kernel and OpenJDK libraries among other components) but doesn't use GPLv3 for multiple reasons.
AOSP used to use a lot of GPLv3 code as part of the toolchain for building AOSP but that was replaced with LLVM, ToyBox and other permissively licensed projects.
German courts are not bound by precedent in the same way as US courts and you're referring to a specific case in Germany which cannot be broadly applied.
AOSP ships a lot of GPLv2 code (Linux kernel and OpenJDK libraries among other components) but doesn't use GPLv3 for multiple reasons.
AOSP used to use a lot of GPLv3 code as part of the toolchain for building AOSP but that was replaced with LLVM, ToyBox and other permissively licensed projects.