- Please use a more explicit name for the archive:

Source0:        https://github.com/icecc/icemon/archive/v%{version}/%{name}-%{version}.tar.gz

 - Please justify the patch or link to an upstream PR/commit:

# Backport of docbook -> asciidoc from upstream
# https://github.com/icecc/icemon/commit/479490ffbe0d13ed3059b67241671cb78521a10a
Patch1:         icemon-asciidoc.patch

 - The SPEC must be updated to the latest CMake guidelines, see https://docs.fedoraproject.org/en-US/packaging-guidelines/CMake/

%build
%cmake
%mcake_build

%install
%cmake_install

[…]

%check
%ctest

 - Use https:

URL:            https://kfunk.org/tag/icemon/

 - End your description with a period;

%description
A GUI monitor for Icecream, a distributed compiler system.

 - The manpage should not be installed with %doc, and the manpage extension should be globbed as the compression may change in the future:

%{_mandir}/man1/icemon.1.*

 - This could be simplified:

%{_datadir}/icons/hicolor/22x22/apps/icemon.png
%{_datadir}/icons/hicolor/16x16/apps/icemon.png
%{_datadir}/icons/hicolor/48x48/apps/icemon.png
%{_datadir}/icons/hicolor/128x128/apps/icemon.png
%{_datadir}/icons/hicolor/32x32/apps/icemon.png

→

%{_datadir}/icons/hicolor/*/apps/icemon.png

 - Consider providing an Appdata file and validate it: https://docs.fedoraproject.org/en-US/packaging-guidelines/AppData/

 - Add CHANGELOG.md and README.md to the %doc

%doc CHANGELOG.md README.md

Thanks, in fact you did all the hard work.

Spec URL: http://people.redhat.com/jkratoch/icemon.spec
SRPM URL: http://people.redhat.com/jkratoch/icemon-3.3-6.fc34.src.rpm
metainfo: https://people.redhat.com/jkratoch/icemon.metainfo.xml

There is one issue but it works now:
# FIXME: This command would install it to /usr/share/appdata .
# DESTDIR=%{buildroot} appstream-util install %{SOURCE1}
install -m644 -D %{SOURCE1} %{buildroot}/%{_metainfodir}/%{name}.metainfo.xml

LGTM, package approved.