on a newly installed Tumbleweed system, 'zypper install zim' pulls just
'zim-lang' with it. However, when running zim the following error is thrown.

Traceback (most recent call last):
  File "/usr/bin/zim", line 130, in <module>
    main()
  File "/usr/bin/zim", line 104, in main
    import zim.main
  File "/usr/lib/python3.8/site-packages/zim/main/__init__.py", line 31, in
<module>
    from zim.notebook import Notebook, Path, \
  File "/usr/lib/python3.8/site-packages/zim/notebook/__init__.py", line 43, in
<module>
    from .info import NotebookInfo, NotebookInfoList, \
  File "/usr/lib/python3.8/site-packages/zim/notebook/info.py", line 18, in
<module>
    from .notebook import NotebookConfig, _resolve_relative_config
  File "/usr/lib/python3.8/site-packages/zim/notebook/notebook.py", line 17, in
<module>
    import zim.templates
  File "/usr/lib/python3.8/site-packages/zim/templates/__init__.py", line 61,
in <module>
    from zim.templates.functions import build_template_functions
  File "/usr/lib/python3.8/site-packages/zim/templates/functions.py", line 24,
in <module>
    from zim.formats.html import html_encode
  File "/usr/lib/python3.8/site-packages/zim/formats/__init__.py", line 78, in
<module>
    from zim.plugins import PluginManager
  File "/usr/lib/python3.8/site-packages/zim/plugins/__init__.py", line 50, in
<module>
    from zim.actions import hasaction
  File "/usr/lib/python3.8/site-packages/zim/actions.py", line 36, in <module>
    PRIMARY_MODIFIER_MASK = _get_modifier_mask()
  File "/usr/lib/python3.8/site-packages/zim/actions.py", line 30, in
_get_modifier_mask
    gi.require_version('Gtk', '3.0')
  File "/usr/lib64/python3.8/site-packages/gi/__init__.py", line 126, in
require_version
    raise ValueError('Namespace %s not available' % namespace)
ValueError: Namespace Gtk not available

'zypper install gtk3-devel' solves this issue by pulling other required
dependencies.

atk-devel at-spi2-atk-devel at-spi2-core-devel bison bison-lang cairo-devel
dbus-1-devel fontconfig-devel freetype2-devel fribidi-devel gdk-pixbuf-devel
gettext-its-gtk4 gettext-tools glib2-devel glibc-devel graphite2-devel
gtk3-devel harfbuzz-devel libblkid-devel libbrotli-devel libbz2-devel
libdatrie-devel libepoxy-devel libexpat-devel libffi-devel libglvnd-devel
libicu-devel libmount-devel libpcre16-0 libpcre2-32-0 libpcre2-posix3
libpcrecpp0 libpcreposix0 libpixman-1-0-devel libpng16-compat-devel
libpng16-devel libselinux-devel libsepol-devel libstdc++6-devel-gcc11
libstdc++-devel libthai-devel libuuid-devel libX11-devel libXau-devel
libxcb-devel libxcb-screensaver0 libxcb-xf86dri0 libxcb-xtest0 libxcb-xvmc0
libXcomposite-devel libxcrypt-devel libXcursor-devel libXdamage-devel
libXext-devel libXfixes-devel libXft-devel libXi-devel libXinerama-devel
libxkbcommon-devel libXrandr-devel libXrender-devel libXtst-devel
linux-glibc-devel m4 Mesa-KHR-devel Mesa-libEGL-devel Mesa-libGL-devel
pango-devel pcre2-devel pcre-devel typelib-1_0-Atk-1_0 typelib-1_0-Atspi-2_0
typelib-1_0-GdkPixdata-2_0 typelib-1_0-Gtk-3_0 wayland-devel
wayland-protocols-devel xorgproto-devel zlib-devel

and these two automatically recommended packages
bison-lang libpng16-compat-devel

Afterwards, Zim can run successfully as expected. 

The normal behaviour should be, by installing zim package, zypper pulling all
these other required dependencies with it in order to run zim successfully.