Footnotes keyboard shortcut in Libre Office

This shortcut is not set by default: Shortcut Keys for LibreOffice Writer – LibreOffice Help so you need to create your own customized shortcut:

1. Tools | Customize.
2. Keyboard tab.
3. In Shortcut window select keyboard shortcut combination you would like to have.
4. From Category window select Insert.
5. From Function window select Footnote/Endnote.
6. Click on Modify button.
7. Click on OK button to close dialog.
8. Execute keyboard shortcut you defined.