Saved over a game file but can access it on my old Xbox.

Can you clarify? Do you mean I should try to do what I’m hesitant to do which is, unplug Wi-Fi, load up old save on the Xbox one, plug in Wi-Fi and save the game, load up the Xbox X and hope that it transfers over?

Hi Joseph, I'd love to help.

Unfortunately, none. When you connect the Xbox one to the internet, the game should ask him again if what game save he would like to use.

You may refer here: https://support.xbox.com/help/games-apps/game-s...

Just to give you a proper expectation, this doesn't guarantee that he'll still be asked again, worst, the one that was synced to the cloud from the new console will be the one that will sync.

I haven’t done anything yet, I don’t want him to lose the save on the old Xbox if it syncs. Is there possibly something I could do with a flash drive? Like unplug Wi-Fi, plug in Xbox one, save the save to a flash drive then load it up on the Xbox X?

To answer your question yes, as it is the only way to sync local console saves to the cloud for you to be able access your saves to other consoles. To avoid this from happening again in the future I would suggest to always select the correct save progress.

Sadly, that wouldn't be possible, though, as mentioned, you can only try connecting the console to the internet for the local saved data to sync to the cloud.