{1..10} is a bash feature, it is not defined in POSIX sh.

It seems that subprocess.check_output("./test.sh", shell=True) invokes sh in your second example (Linux) and bash (or another shell which supports this feature) in the first example (macOS).

See:

• https://www.shellcheck.net/wiki/SC3009
• Actual meaning of 'shell=True' in subprocess
• Does the `shell` in `shell=True` in subprocess means `bash`?