The mcomix spec contains the line:

Recommends:     unrar

in order to open the archive compressed with rar. However it is quite common to
have comics compressed with 7z or in pdf format.

I suggest to add these lines to the spec file:

Recommends:     mupdf
Recommends:     p7zip

Also when I start mcomix I can see these messages:

[MainThread] WARNING: subprocess32 not available! using subprocess
[MainThread] WARNING: czipfile not available! using zipfile

It would be good to add as well:

Recommends:     python2-subprocess32

About python2-czipfile, such rpm is not packaged yet in opensuse.
It may well be in the near future (one year ago python2-subprocess32 was not
available as well).
When python2-czipfile became available in opensuse, then mcomix coulds also:

Recommends:     python2-czipfile