I am not sure what x-widget push-button means exactly, but if they are just buttons then we can achieve the same effect with default (text-)buttons.
This is used in the sketch-mode package (which just now arrived on elpa) for showing previews of fonts.

On Thu, 21 Oct 2021 at 00:57, Richard Stallman <rms@gnu.org> wrote:
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  > I remember a proprietary version of Emacs (not derived from GNU Emacs)
  > having the ability to display arbitrary X Toolkit (such as Motif or
  > Athena widgets) widgets inside frames, along with providing protocol
  > bindings to X-Windows.

That feature could pose ethical/legal problems of linking with nonfree
widgets.

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Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
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