I have a NIV Schofield Bible with red letters for the voice of Jesus. Rev 21:5-8 does not have red letters (emphasis mine)
5 He who was seated on the throne said, “I am making everything new!” Then he said, “Write this down, for these words are trustworthy and true.”
6 He said to me: “It is done. I am the Alpha and the Omega, the Beginning and the End. To the thirsty I will give water without cost from the spring of the water of life. 7 Those who are victorious will inherit all this, and I will be their God and they will be my children. 8 But the cowardly, the unbelieving, the vile, the murderers, the sexually immoral, those who practice magic arts, the idolaters and all liars—they will be consigned to the fiery lake of burning sulfur. This is the second death.”
But Rev 22 has two passages that are red. Particularly verses 12-16 (emphasis mine)
12 “Look, I am coming soon! My reward is with me, and I will give to each person according to what they have done. 13 I am the Alpha and the Omega, the First and the Last, the Beginning and the End.
14 “Blessed are those who wash their robes, that they may have the right to the tree of life and may go through the gates into the city. 15 Outside are the dogs, those who practice magic arts, the sexually immoral, the murderers, the idolaters and everyone who loves and practices falsehood.
16 “I, Jesus, have sent my angel to give you[a] this testimony for the churches. I am the Root and the Offspring of David, and the bright Morning Star.”
They each say the same thing and there is a clear implication that the person in Rev 21 is God. Is there any indication why some scholars would think that person is anyone else?