I'm not sure I understand that comment. Docker isn't virtualization at least as the term is normally used (of a full OS running in a virtual machine). It's containerization and, to the degree it's terrible (I haven't used it much), it may be related to the fact that MacOS is based on BSD and not Linux.
Big Sur apparently has native Mac virtualization for, initially, x86 although I'm unclear what the underlying tech and a query or two at the time of the original announcement didn't yield any results. So that may improve Linux virtualization.
As for ARM, virtualization is not emulation. There's going to be Rosetta 2. But my understanding is that you shouldn't expect x86 Linux to run on Mac ARM using virtualization, Docker, or anything else. (Apple demoed an ARM build of Linux running in a VM on ARM at WWDC.)