The function lower was applied to the command line before trying to execute the script, causing the file not to be found on Linux and MacOS (while windows file names are not case sensitive).
I fixed this bug here: https://github.com/brainstorm-tools/brainstorm3/commit/f3c58de81e18c092d2d884e2d7b86d3ffedab256
I will post updated compiled versions of Brainstorm later today (2022b and 2020a).
Thanks for reporting this issue.