I fixed it, you have to edit the xml files in /usr/share/themes/Artix-dark/metacity-1/
(do a backup first)
in metacity-theme-1.xml and metacity-theme-2.xml (they are identical), I changed
this:
<frame_geometry name="borderless" has_title="false" rounded_top_left="false" rounded_top_right="false" parent="normal" >
<distance name="left_width" value="0" />
<distance name="right_width" value="0" />
<distance name="bottom_height" value="0" />
<distance name="title_vertical_pad" value="0" />
<border name="title_border" left="0" right="0" top="0" bottom="0" />
<border name="button_border" left="3" right="3" top="0" bottom="0"/>
</frame_geometry>
to this:
<frame_geometry name="borderless" has_title="false" rounded_top_left="false" rounded_top_right="false" parent="normal" >
<distance name="left_width" value="0" />
<distance name="right_width" value="0" />
<distance name="bottom_height" value="0" />
<distance name="left_titlebar_edge" value="0"/>
<distance name="right_titlebar_edge" value="0"/>
<distance name="button_width" value="0"/>
<distance name="button_height" value="0"/>
<distance name="title_vertical_pad" value="0" />
<border name="title_border" left="0" right="0" top="0" bottom="0" />
<border name="button_border" left="0" right="0" top="0" bottom="0"/>
</frame_geometry>
and in metacity-theme-3.xml I changed this:
<frame_geometry name="border" has_title="false" rounded_top_left="false" rounded_top_right="false" parent="normal" >
<distance name="left_width" value="1" />
<distance name="right_width" value="1" />
<distance name="bottom_height" value="1" />
<border name="title_border" left="10" right="10" top="0" bottom="0" />
<border name="button_border" left="3" right="3" top="0" bottom="0"/>
<distance name="title_vertical_pad" value="1" />
</frame_geometry>
<frame_geometry name="borderless" has_title="false" rounded_top_left="false" rounded_top_right="false" parent="normal" >
<distance name="left_width" value="0" />
<distance name="right_width" value="0" />
<distance name="bottom_height" value="0" />
<distance name="title_vertical_pad" value="0" />
<border name="title_border" left="10" right="10" top="0" bottom="0" />
<border name="button_border" left="3" right="3" top="0" bottom="0"/>
</frame_geometry>
to this:
<frame_geometry name="border" has_title="false" rounded_top_left="false" rounded_top_right="false" parent="normal" >
<distance name="left_width" value="1" />
<distance name="right_width" value="1" />
<distance name="bottom_height" value="1" />
<distance name="left_titlebar_edge" value="0"/>
<distance name="right_titlebar_edge" value="0"/>
<distance name="button_width" value="1"/>
<distance name="button_height" value="1"/>
<distance name="title_vertical_pad" value="1" />
<border name="title_border" left="0" right="0" top="0" bottom="0" />
<border name="button_border" left="0" right="0" top="0" bottom="0"/>
</frame_geometry>
<frame_geometry name="borderless" has_title="false" rounded_top_left="false" rounded_top_right="false" parent="normal" >
<distance name="left_width" value="0" />
<distance name="right_width" value="0" />
<distance name="bottom_height" value="0" />
<distance name="left_titlebar_edge" value="0"/>
<distance name="right_titlebar_edge" value="0"/>
<distance name="button_width" value="0"/>
<distance name="button_height" value="0"/>
<distance name="title_vertical_pad" value="0" />
<border name="title_border" left="0" right="0" top="0" bottom="0" />
<border name="button_border" left="0" right="0" top="0" bottom="0"/>
</frame_geometry>
Can you test it?
Why are the registrations here (https://gitea.artixlinux.org/nous/artix-dark-theme/src/branch/master/usr/share) disabled?