M-x setenv RET MANOPT RET -X100-12 RET M-x man RET man RET

This command shows the manual page for man in a new gxditview window. 
Emacs cannot display the manual page because it has not been rendered to 
text. But the error message is "Can't find the cat manpage". The message 
is wrong. Emacs did not try to find the cat manpage, it tried to 
retrieve it and it did not work.

On 19.01.2024 14:32, Eli Zaretskii wrote:
>> Date: Fri, 19 Jan 2024 12:46:57 +0000
>> Cc:manuel@ledu-giraud.fr,68583@debbugs.gnu.org
>> From: Christopher Yeleighton<giecrilj@stegny.2a.pl>
>>
>> If the code in man.el tried to find the manual page by itself, it would
>> not fail because the manual page is there. It succeeds if MANOPT is not
>> set and my MANOPT should not affect the manual page search algorithm.
> That depends on how we try to find the manual page(s).  The
> implementation calls 'man' in a special way, which evidently fails
> under the value of MANOPT you set.