Looks like this topic hasn’t come up in a couple of years, so to save other newbies the drama:
The current Joulescope UI (macOS 12 & 13 | Intel x86_64 | version 0.10.10) wont run on macOS Big Sur 11.7.1. Double-clicking it just hangs forever unresponsive in the Dock without showing any UI, and needs to be force quit. Running joulescope_launcher from the command line instead shows the definitive reason:
File "joulescope_ui/update_check.py", line 91, in _platform_name
RuntimeError: unsupported macOS version 11.7.1
[18620] Failed to execute script '__main__' due to unhandled exception: unsupported macOS version 11.7.1
The “macOS 10.15 | Intel x86_64” variant on the other hand, runs fine.