Generally the religion can be broken into usool and furoo (although some scholars don’t like this classification, others have allowed it).
Usool: Things from aqeedah which must be known, such as Allah is above His Throne, the pillars of emaan and things from fiqh such as there are 5 daily prayers, Fajr salaah is 2 rak’ah and so on. In these there can be no difference of opinion.
Furoo: Issues in which there can be differing in.
The difference shouldn’t cause disunity as these are issues where a difference has occurred in the past and is usually a Sunnah action, whereas the Ummah remaining united is obligatory.
An example of this is Ibn Taymiyyah (rh) who mentions that a person can leave Sunnah of prayer for unity purposes.
And Allah Knows best.