What does Black Square Button look like on Facebook?

On Facebook it is the design shipped in 16.0, shown above at full size. Older revisions are listed beneath it.

When did Facebook add Black Square Button?

Facebook first drew Black Square Button in 1.0, released January 31, 2014.

Meta Platforms, Inc. has shipped 13 versions of Black Square Button. Each is dated, so you can see when the design changed.

Facebook 2.2

This is the design Facebook introduced in 2.0, shipped again unchanged. It was not redrawn for this release.

✳ marks a release that redrew this emoji. The rest re-shipped the design unchanged.

What does Black Square Button look like on Facebook?: On Facebook it is the design shipped in 16.0, shown above at full size. Older revisions are listed beneath it.
When did Facebook add Black Square Button?: Facebook first drew Black Square Button in 1.0, released January 31, 2014.
How many times has Facebook redrawn Black Square Button?: Meta Platforms, Inc. has shipped 13 versions of Black Square Button. Each is dated, so you can see when the design changed.