Based on here,

After Nemo file manager installation, set Nemo as default File-Manager and allow desktop handling by Nemo open Terminal (Press Ctrl+Alt+T) and copy the following commands in the Terminal:

xdg-mime default nemo.desktop inode/directory application/x-gnome-saved-search

gsettings set org.gnome.desktop.background show-desktop-icons false

gsettings set org.nemo.desktop show-desktop-icons true

Now enter this command in terminal to check that now Nemo is your default file manager :

xdg-mime query default inode/directory

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If you want to go back with Nautilus as default File Manager try these commands:

xdg-mime default nautilus*.desktop inode/directory application/x-gnome-saved-search

gsettings set org.nemo.desktop show-desktop-icons false

gsettings set org.gnome.desktop.background show-desktop-icons true