"f" logo for <a href="https://en.wikipedia.org/wiki/Facebook" class="extiw" title="w:Facebook">Facebook</a> as acquired from the HTML+SVG source of a page on facebook.com. 2021 date in filename is <i>not</i> suggestive of when logo first came to be used, merely the year the logo was acquired and uploaded (a more definitive date may be possible by checking on archive.org).
Facebook
www.facebook.com