Does one become a disbeliever if they do not move a Qur'an placed in its stand away from the extension of feet, knowing that scholars like Al-Fawzan and Ibn Uthaymeen, may Allah have mercy on them, have issued fatwas prohibiting extending the feet towards a nearby Qur'an, and it has been reported that whoever leaves the Qur'an in filth while being able to remove it becomes a disbeliever?

The jurists differed on the ruling of extending one's legs towards the direction of the Mushaf (Qur'an). Some of them disliked it, and some prohibited it.

However, if the location of the Mushaf is not directly opposite to the direction of the outstretched legs, such as if it is elevated or lowered, or if the legs are turned away from it to the right or left, then there is no harm in that.

As for what happens to some worshippers who extend their legs towards the stand holding the Masahif (Qur'ans) during prostration, there is no harm in it, as there is no intention of disrespect.

Based on this, you are not obligated to move the Mushaf away from behind the worshippers, and you will not fall into disbelief if you do not do so.