First Test:

$ kioclient exec 'man:cat'

Result of test:
Konqueror opens:

This site can’t be reached

The webpage at error:/?error=106&errText=man#man:cat might be temporarily down or it may have moved permanently to a new web address.
ERR_UNKNOWN_URL_SCHEME

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Second Test:
$ kioclient5 exec 'man:cat'

Result of second test:

ErrorWindow opens:

WindowTitleBar: Error KIO Client
WindowContentPane: Could not find any application or handler for man:cat

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Third Test:

In 'Help Center': No 'Unix Manual Pages', only errors.

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Can anybody confirm these results?

Thank You, in advance.