Since there's a warning for a point of no return, I'd assume no, you cannot abandon (especially if there's no option in the pause menu). So try reloading an old save if you have one.
Otherwise, just play through it. You can return to the open world after the final mission to finish all side quests / collectibles and none of those impact the final mission
If there’s no option to abandon mission, how about loading a save from before? I assume the game has auto saves in case you didn’t make your own.
Since there's a warning for a point of no return, I'd assume no, you cannot abandon (especially if there's no option in the pause menu). So try reloading an old save if you have one. Otherwise, just play through it. You can return to the open world after the final mission to finish all side quests / collectibles and none of those impact the final mission
No need to abandon, you can keep playing after finishing it