Revelation 21:6

Greek Γέγοναν ἐγὼ τὸ Ἄλφα καὶ τὸ Ὦ

Γέγοναν is a verb meaning "they have become/they happened." It does not mean "it is done". See Strong's #G1096.

The glaring third person plural "they became" and the absence of the verb εἰμι "I am" was quite troublesome for translators so they thought to place a period between the words "Γέγοναν ἐγὼ" which on its own means quite simply, "They have become I/myself." A great many translates additionally altered the third person plural of Γέγοναν and rendered it as a singular "it happened" or "it is done."

"I am" as rendered by all the translations we have seen is an untrue translation and an insertion of a word that does not exist. It was difficult enough to understand that some later manuscripts went so far as to plug it in, as indicated by the bracketed word [εἰμι]. It does not say "I am the Alpha and the Omega." Truthfully, it reads, "they have become/happened I/myself the Alpha and the Omega"