Help! I've been searching for this movie for years: time travel, betrayal, and the end of time/world!

If you could please help me find the title of the movie, I would be really grateful. Thank you so much in advance for the help! 🙏

Hello everyone!!! I am desperately looking for a science fiction movie that has been haunting me for years. I saw it some time ago, but I vividly remember some scenes, although the title completely escapes me. I hope you can help me solve this mystery. The movie is about a group of people who travel through time from the present to the past. I remember that the cars in the “past” were typical of the time and that the “main characters” used a “time machine” to travel. • The mission and precautions (key detail): The group had a mission in the past, although I do not remember the specific details. The mission was considered very dangerous and there was a lot of tension among the members. They had received strict instructions: no modern weapons were to be carried into the past and they were not allowed to interact with people to avoid risking altering the timeline. Also, they were not to carry or leave modern objects or perform actions that could alter the course of events. • During the mission: At the beginning of the film or just before time travel, the character who will turn out to be the traitor wanted to carry a modern weapon. The rest of the group prevents him from doing so, explaining the risks of altering the present. • Betrayal (final scene): Immediately after returning to the present and while celebrating the success of the mission, one of them, a member of the group, betrays them. The betrayal occurs suddenly and unexpectedly. The group realizes the traitor's intentions only when it is too late: he has already entered the time machine and is about to leave again. They tried to stop him, but it was impossible. He was very quick and cunning. He acted stealthily and caught everyone by surprise, even though they were close. By the time the group realized what was happening, it was too late: he had left for the past. This character uses the same machine to go back in time. This is a crucial point that I remember well: the betrayal happens almost immediately after the return and success of the mission. • The scene on the road (another key point and description of the weapon, final scene): The traitor is on a wide road. The setting was urban: a large city. The traitor carried and used a modern weapon: perhaps a grenade or a pistol, I don't remember the exact model, but it was clearly a weapon that did not belong to the era. • Weapons, destruction, and impact on time (the ending and key to the film): The traitor uses the modern weapon (perhaps a grenade or gun) and causes instant and total destruction of time/world. You could see that time/world was vanishing, as if it was being erased. It was a very eerie visual effect. The destruction manifested as a fading, a gradual vanishing of reality. It was as if time itself was retreating, taking everything away. An effect of erasure. The whole world seemed to dissolve into nothingness, as if time itself was self-eliminating. I am not sure if it caused the total destruction of the world or if it simply altered the present, creating a new timeline whose consequences we do not see. The destruction begins down the road in the background and spreads until time itself is completely annihilated. • Bottom line: The film ends with this very scene of destruction/deletion/disappearance. We do not see the long-term effects of the present and past, but only the most drastic and immediate consequence. Subsequent to this event (of time elimination), moments later, the film ends. If you can please help me find the title of the film, I would really appreciate it. Thank you very much in advance for your help! 🙏 Note: This comment was created from a merged conversation originally titled Help. I've been looking for this movie for years: time travel, betrayal, and the end of time/world!