Acts 4:24 And when they heard it, they lifted their voices together to God and said, “Sovereign Lord, who made the heaven and the earth and the sea and everything in them,
1 Timothy 6:15 which he will display at the proper time—he who is the blessed and only Sovereign, the King of kings and Lord of lords,
What is to be displayed according to the only Sovereign?
1 Timothy 6:14 mentions Christ’s second coming. My question here is that the opening passage indicates there is only one Sovereign and He who sits on that throne is Jesus Christ who is identified as King of kings and Lord of lords, was Father God ever Sovereign?
The logical answer is that when any sovereign act ever occurred the Father and the Son were One.
What surprised me in this bible study was that in the ESV the only time the title was used is in the New Testament.

For many years the KJV was the standard for bible translations. The Greek word in Acts 4:24 is δεσπότης despótēs, des-pot’-ace; perhaps from G1210 and πόσις pósis (a husband); an absolute ruler (“despot”):—Lord, master.
The word sovereign is used as an adjective to Lord which identifies a change is His participation in the New Covenant where He takes on one more identity, that of a husband. Absolute rule was never in question but once He ascended to the right hand throne of God and having everything turned over to rule with absolute power, He did so as our betrothed.