In Revelation 5, John weeps bitterly (or convulsively) for no one is found worthy to open the scroll. The passages are clear that nobody in Heaven, on Earth, nor under the Earth was (or is) worthy. Where then was Jesus before He appeared and took the scroll? John seems to indicate that the Lamb appeared freshly slain. So was John taken back to crucifixion? It seems while Jesus was on the cross bearing sin, He wouldn’t be technically worthy. Or was John in the future, and at the time John was weeping Jesus was in transit to the Father and was not found at that particular moment.
I don’t see anything in Rev. 5:6 that requires the Lord to have been freshly slain. The literal translation speaks of a Lamb “as it had been slain.” The words “had been” are in the past perfect tense indicating the act of slaying Him took place in the past and was over. Many scholars interpret the phrase “Lamb as it had been slain” as meaning the Lord will still be in human form and will bear the scars of His ordeal.
And you’re correct in saying that He wasn’t really “worthy” until after the resurrection when His act of redemption was proven to be complete. I don’t think the verses leading up to Rev. 5:6 are intended to imply that Jesus is not present. I think they serve the purpose of confirming that in all of creation Jesus is the only one who can open the scroll and begin the end times judgments that will culminate in His return as King of the whole Earth (Zechariah 14:9).