Cinema R26 uses the AVX instruction set on x86_64 (Intel/AMD) CPUs.
As Rosetta is only supporting Intel CPUs up to the SSE instruction set, it's not possible to run Cinema R26 in emulation mode on the M1.
Basically, this means S26 can not run in Rosetta, but for those needing Cinema 4D to run in Rosetta for the Substance pipeline, M1 support will be coming in a future update.
In the meantime, if you need to use the Substance pipeline, R25 will run in Rosetta, allowing you to continue using the Substance pipeline until we've added M1 support for Substance in Cinema 4D S26.
You can download R25 here: