“Okay, it’s been churning for 15 hours. My old MacBook Air is 12 years old (2013). Is that the reason it’s so slow in transferring info? Maybe it’s too old to complete the transfer. Then what? What would Apple geniuses suggest?“
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Use Migration Assistant:
IDK. I don’t work for Apple. But over the years, waiting out a transfer is the best. How exactly are you performing this migration? Are you using Migration Assistant? That is what to use here. If it were stalled, and hardware is getting hot, I’d place it on a laptop cooler. If things are hot, I’d give Apple a call. Discontinuing this, you might get some errors when restarting your Mac. And that might come down to reinstalling the MacOS. But, before restarting, create a Time Machine Backup of your Mac; that way, you’ll have something to restore it from, should anything go wrong after the restart.