Yes but I don't believe it, thinking his second coming already happened makes our own future

John 21:22-23 doesn't say John will live until Jesus returned like the link says it does. Literally clearly says as clear as day that he did not tell John he would not die, Jesus told Peter to mind his own business and focus on his own ministry.

John 21:22
Jesus saith unto him, If I will that he tarry till I come, what is that to thee? follow thou me.

John 21:23
Then went this saying abroad among the brethren, that that disciple should not die: yet Jesus said not unto him, He shall not die; but, If I will that he tarry till I come, what is that to thee?

And then for the "generation shall not pass" verses, they're always in the context of the world itself passing away, so generation clearly means the world and everybody in it, and that fits with the rest of Bible prophecy.

Mark 13:30
Verily I say unto you, that this generation shall not pass, till all these things be done.

Mark 13:31
Heaven and earth shall pass away: but my words shall not pass away.

"The 2nd coming of Christ already happened"has a lot of holes in it and then it gives a ton of uncertainty for "what about us today?" That are completely unanswered.