I understand! A dedicated conda environment might satisfy your requirement of isolating ROOT and the software that sits on top of it from the rest, but if “the rest” is not packaged with conda it might be annoying.
For Docker on Apple M1: looking at the Docker docs that @James-Carroll shared, you should be able to start from a ARM64 or multi-arch image and compile ROOT in there (ROOT compiles on ARM and it can be installed on Raspberry Pi’s, for instance – there are some forum posts about some tweaks that might have to be applied).
Cheers,
Enrico