…but hospitable, loving what is good, sensible, just, devout, self-controlled…
Titus 1:8 (emphasis mine)

Just can mean righteous or upright. It includes being proper, fair and equitable.

In describing the leader, the term focuses on behavior that is just, fair and inherently honest in dealing with people.1

There is no room for an elder to show favoritism. He must be thoroughly biblical in all his dealings with others. There is always a danger for elders to treat people differently because of their social or economic status. This must always be avoided.

The Lord favors those who deal righteously and he is opposed to those who are evil.

FOR THE EYES OF THE LORD ARE TOWARD THE RIGHTEOUS, AND HIS EARS ATTEND TO THEIR PRAYER, BUT THE FACE OF THE LORD IS AGAINST THOSE WHO DO EVIL.
1 Peter 3:12

When the elder demonstrates righteousness, he gives testimony to the fact that he is a child of God.

If you know that He is righteous, you know that everyone also who practices righteousness is born of Him.
1 John 2:29

1 Towner, P. H. (2006). The Letters to Timothy and Titus (pp. 689–690). Grand Rapids, MI: Wm. B. Eerdmans Publishing Co.