Hello @felmue,
I found some additional information on the M5Stack homepage (https://docs.m5stack.com/#/en/faq).
"Q36: Is Core2 compatible with other modules
The depth of Core2's M-Bus terminal is different from standard Cores. For modules which odered AFTER Core2 release are all compatible; For those earlier than the date (Sep 1st, 2020), need to consult with us before applying."
Thanks
Helge