And as https://www.openwall.com/lists/oss-security/2024/03/29/4 says:
"These conditions include targeting only x86-64 linux: [...] Building with gcc and the gnu linker [...] Running as part of a debian or RPM package build:"
I'm not an expert of course.
I think it is gigabits per second, but to be clear: Whatever dd reports as speed after finishing (or with status=progress)