For those of us old timers still using CVS... The error says how to fix (perl 5.26 on Suse Leap 15.1). Seems OK with this 1 liner, I've come across several similar issues elsewhere in old perl scripts.
Error - Perl execution failed
Can't use 'defined(@array)' (Maybe you should just omit the defined()?) at /usr/libexec/webmin-1.910/pserver/cvsweb.cgi line 1967.
Which Webmin version are you running there? This should be fixed already ..
Using latest - 1.91. Perhaps it didn't upgrade at last update if as you say already fixed ?
Try applying this patch : https://github.com/webmin/webmin/commit/bf63fea503f135d23fc1b5be18260f2ec4b1c4ed#diff-6b84611d25b352a7b54c591c87e79865
Fixed - thanks