Nikolai2038 Thanks for putting some life into this issue again.
I tried to create both settings.ini
files, but nothing changed after restarting Nemo.
Triggered by your response I started a new search and this time I stumbled upon an issue at askubuntu.com: https://askubuntu.com/questions/1318002/why-are-all-button-and-menu-icons-gone.
I tried the command from the first answer in this issue:
gsettings set org.gnome.settings-daemon.plugins.xsettings overrides "{'Gtk/ButtonImages': <1>, 'Gtk/MenuImages': <1>}"
and to my great satisfaction after a restart Nemo now shows all desired icons! I could reproduce it at a few other Solus installs, so it seems quite consistent.
I also discovered that already many years ago a long discussion has taken place about the removal of this setting from org.gnome
and that it has been removed deliberately because of the (often criticized) philosphy of our Gnome developer friends 😏 . So I'm not sure about how long this will keep working, but for now I'm happy with it.