What does Stop 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 Stop Button?

Facebook first drew Stop Button in 2.0, released February 20, 2017.

Meta Platforms, Inc. has shipped 12 versions of Stop Button. Each is dated, so you can see when the design changed.

Facebook 4.0

Facebook shipped a new design for Stop Button in 4.0, released April 1, 2019. The previous design is shown beside it.

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

What does Stop 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 Stop Button?: Facebook first drew Stop Button in 2.0, released February 20, 2017.
How many times has Facebook redrawn Stop Button?: Meta Platforms, Inc. has shipped 12 versions of Stop Button. Each is dated, so you can see when the design changed.