What is the difference between the collection process of Al-Qur'an that Abu Bakr followed and the one that Uthman followed (name one difference)?

Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

The most important difference between the collection of the Qur'an done by Abu Bakr and that of Uthman is as follows:
Caliph Abu Bakr collected the Qur'an and wrote it in pamphlets and books in all its seven letters (the seven i.e. ways in which the Qur'an was revealed and which conform to the seven dialects of the Arabs at that time).
However, during the Caliphate of Uthman, all existing copies were called in. In consultation with the Prophet's companions (present at the moment) from among Ansar and Muhajireen an authoritative version (with one dialect) was compiled and sent to all Muslim countries to dispel possible disorder due to different ways of reading among Muslims.
Allah knows best.