Yes — the usual workaround is to pre-focus on something placed where you will stand, then take its place before the timer fires. Put an object at your intended position (for example a lamp, broom handle, or paper target), focus on that object, start the self-timer, remove the object, and stand in exactly the same spot.

If your camera offers manual focus, use it so the focus distance stays fixed. Mark your spot on the floor with tape so you can return to the same distance from the camera each time.

To make focus easier and more forgiving, use a smaller aperture if possible (higher f-number), which increases depth of field. This helps if you move slightly forward or back. Also remember that focus errors are more obvious when you're close to the camera.

So no, self-timer self-portraits are not impossible — you just usually need to pre-focus on a stand-in at the correct distance.