Nico

Also of Modern English usage.
https://www.behindthename.com/name/nico/top/united-states
https://www.behindthename.com/name/nico/top/england-wales
https://www.behindthename.com/name/nico/top/new-zealand

Also Guernésiais: http://dbooks.bodleian.ox.ac.uk/books/PDFs/590676737.pdf
https://nrm.wikipedia.org/wiki/Rimes_guernesiaises

Also Flemish: http://www.names.be/jongensnamen.html?met=Nico&sort=beldesc

Also Afrikaans: https://af.wikipedia.org/wiki/Nico_Carstens
You'll find numerous bearers on social media.

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(It is, however, also an acronym for https://af.wikipedia.org/wiki/National_Independent_Civic_Organisation)

Also a Jèrriais short form of Nicolas: https://www.learnjerriais.org.je/pluginfile.php/3125/mod_resource/content/1/dictionnaithe%20Angliais-J%C3%A8rriais%202012.pdf
http://members.societe-jersiaise.org/geraint/jerriais/noms1ers.html

Feminine use, as in the case of Coldplay member Guy Berryman’s daughter Nico, https://en.m.wikipedia.org/wiki/Guy_Berryman.

This can also be a name for a girl. Singer from Blind Melon, Shannon Hoon, named his daughter Nico. I think it would be nice for a boy or a girl.

"Nico" is also the Spanish short form for "Nicolás".

As people above me have proved, you'll find Nico used more often as a girl's name rather than a boy's.