If the Onyx website is visited...it can clearly be seen that the developers of Onyx (Titanium Software)...always release a version of Onyx that's specific to each version of the macOS. Right now there are 15 different versions of Onyx (each one for a specific version of the macOS).
OnyX is a multifunction utility that you can use to verify the startup disk and the structure of its system files, perform cleaning and computer maintenance tasks, configure some hidden parameters of many Apple applications, and more.
www.titanium-software.fr
Right now the latest version of Onyx is compatible with macOS 11 (Big Sur)...and ONLY compatible with Big Sur (no other versions of the macOS). Thus there should be no expectation that it would be compatible with the next macOS release (Monterey).
When macOS "Monterey" is released...I'm confident Titanium Software will release a version of Onyx specifically for Monterey!
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