the whole building falling onto Thanos into a flock of crow... its not illusion as the substances really does change into whatever he is changing it into.

The whole moon blowing and bringing it down to the surface of Titan... was done using the power of Power Stone.. also Devouring the power Dr. Strange sent to him and changing it into a moving black hole.. that's Power Stone as well..

easy, remember how Wong chop off Cull Obsidian arm with teleportation? Say spidey pull thanos arm to portal and Dr Strange close it. Done!

Physicist theorized time travel came in 2 forms. Single loop that adhere to grandfather's paradox. Infinite loop that has endless parallel realities. Any changes in timeline will just branch off another reality. Comicbooks gave it a fancy name called Multiverse. Like what was demonstrated on Rick and Morty, Looper, Fringe, etc... To make it "idiot proof" you focus on the timeline that matters narratively otherwise it's a slippery slope to tell a story out of it.

The bigger issue I had is stealing gemstones from different timelines does not create nuclear butterfly effects. "Primer" demonstrated how difficult it is not to sets off butterfly effect. They oversimplified it by returning the stones to respective timelines. The million dollar question is the act of snapping, does it erase Thanos from an all encompassing existence or only in the Endgame instance or maybe I wasn't paying enough attention when Hulk mansplaining it to Ancient One. If they only wipe Thanos from Endgame timeline meaning events post GOTG1 will take a different path that has nothing to do with Thanos influence. That's an alternate reality already.

Moral of the story is there's no simple way to do a time travel storyline without butchering factual time displacement depiction.