This is a mix of Adwaita symbolic icons and new icons that we made together with my friend. Icons match and don't get out from the style of Adwaita icons.

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Mono icons

Download

Download icons here.

Installing

To install icons, place the folder in the ~/.icons directory and select icons in Gnome Tweaks. In order for icons to work everywhere, including for flatpak apps, go to the directory where you saved the folder and move the icons folder to /usr/share/icons.
Command:

sudo cp -r MonoIcons /usr/share/icons

If you don't want to use the default app icons, move the icons from your favorite icon pack to scalable/apps.

Uninstalling

To remove icons, delete the icons folder in ~/.icons and select the other icons in Gnome Tweaks. Go to /usr/share/icons and open a terminal.
Command:

sudo rm -r MonoIcons