Also removed one whitespace character to hopefully fix the Checking EditorConfig error:

pkgs/applications/networking/cluster/lens/default.nix:
	24: Trailing whitespace

Nothing happens when I click any of the documentation links on the right pane when adding a cluster, or when I click the items in the help menu (except What's new).
Stderr doesn't show messages about this, but it seems like it can't browser windows (unlike xdg-open https://nixos.org which does work in my environment)

Thanks for building and trying it out!
I did a fresh rebuild, and removed my ~/.config/Lens directory to make sure I had a clean environment, but unfortunately I can't reproduce those problems with the links not opening. I'm on GNOME 3 for background.

I'm also on GNOME 3. My normal user doesn't get any logs but I've tried it on a clean user with firefox in its profile (nix-env -i) and got this when clicking links:

/nix/store/2jysm3dfsgby5sw5jgj43qjrb5v79ms9-bash-4.4-p23/bin/bash: symbol lookup error: /usr/lib/libc.so.6: undefined symbol: _dl_fatal_printf, version GLIBC_PRIVATE
/usr/bin/xdg-open: line 883: x-www-browser: command not found
/nix/store/2jysm3dfsgby5sw5jgj43qjrb5v79ms9-bash-4.4-p23/bin/bash: symbol lookup error: /usr/lib/libc.so.6: undefined symbol: _dl_fatal_printf, version GLIBC_PRIVATE
/usr/bin/xdg-open: line 883: iceweasel: command not found
/usr/bin/xdg-open: line 883: seamonkey: command not found
/usr/bin/xdg-open: line 883: mozilla: command not found
/usr/bin/xdg-open: line 883: epiphany: command not found
/usr/bin/xdg-open: line 883: konqueror: command not found
/usr/bin/xdg-open: line 883: chromium: command not found
/usr/bin/xdg-open: line 883: chromium-browser: command not found
/usr/bin/xdg-open: line 883: google-chrome: command not found
/usr/bin/xdg-open: line 883: www-browser: command not found
/usr/bin/xdg-open: line 883: links2: command not found
/usr/bin/xdg-open: line 883: elinks: command not found
/usr/bin/xdg-open: line 883: links: command not found
/usr/bin/xdg-open: line 883: lynx: command not found
/usr/bin/xdg-open: line 883: w3m: command not found
xdg-open: no method available for opening 'https://k8slens.dev/licenses/eula.md'

I'm running NixOS 20.09.

I'm on different system now, but I haven't been able to get the same errors as you yet. 🙁

I do have my configuration.nix in git now if you want to compare.:
https://github.com/dbirks/dotfiles/blob/master/nixos/etc/nixos/configuration.nix

I wonder if something in this section in services is what's making the difference:

    gnome3 = {
      core-os-services.enable = true;
      core-shell.enable = true;
      core-utilities.enable = true;
    };

Thank you! 🏄

Does this work only with Gnome? (I have Plasma and couldn't install lens)

We've tested with gnome, but it shouldn't be gnome-specific. Could you provide the error log?

I hit an error that might be the same as yours:

error: undefined variable 'lens' at /home/david/dotfiles/nixos/etc/nixos/configuration.nix:65:5

I think that's because the nixos-unstable channel has been backed up with a build problem since 9 days ago, before this PR was merged: https://status.nixos.org/

Looks like a fix is on its way though.