Matthew 24:15-20 / Mark 13:14-18 / Luke 21:20-23a are all saying the exact same thing.
And, it is referring to the events of circa 70 A.D.
Impossible since Jesus said that one generation would see all things he described which included second coming and the angels gathering the elect.
Mat 24:29
Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken:
Immediately after the tribulation will the sun and moon go dark and the stars will fall from heaven, all being global events. Did that happen after the Roman's destroyed the city and temple? No.
Mat 24:30
And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory.
All the tribes of the Earth mourning and seeing Christ coming from heaven to the Earth. Again, a global event. Did that happen in Ad70? No.
Mat 24:31
And he shall send his angels with a great sound of a trumpet, and they shall gather together his elect from the four winds, from one end of heaven to the other.
The gathering of the elect by angels in Ad70? No. The disciples would have been the elect of their generation and they certainly weren't gathered by angels. This is the same event known as the Rapture but it didn't happen in Ad70 and hasn't happened yet.
Mat 24:32 Now learn a parable of the fig tree; When his branch is yet tender, and putteth forth leaves, ye know that summer is nigh:
Mat 24:33 So likewise ye, when ye shall see all these things, know that it is near, even at the doors.
Mat 24:34 Verily I say unto you, This generation shall not pass,
till all these things be fulfilled.
"all these things" includes verses 29-31 which shows the second coming and the gathering of the saints. Other scriptures tell us this timeframe is also the time when the dead in Christ are resurrected. Did either of those things take place in Ad70? No.
None of those things happened in the lives of the disciples proving he was NOT talking about their generation not passing before "all these things" occurred.