Roundcube and SOGo (which is used by Mailcow, but hass fewer features than Roundcube) are the only somewhat modern looking options. All the other stuff looks like straight out of the 90s/early 2000s. Nextcloud Mail is pretty good as well.

Fedora, NixOS and Void need a proper wiki like Arch

Most distros could also learn from Arch and create something similar to the AUR. Nix is going in the right direction.

And I guess almost all distros could learn from Artix and Devuan and reconsider if systemd is the right choice.