Generally speaking, you are allowed to bring a small amount of items you buy abroad back to the US without paying duties, as long as you declare them. Looks like that amount is still $800, in spite of this dumb Administration. This doesn't apply to everything, though, you already know about alcohol and tobacco but there may be other things that don't count against that $800, and it's your responsibility to know. (And some things are banned regardless, like fruit and some meat products).

You arw allowed to bring personal items you bought in the US back to rhe US. Back 30+ years ago coming across the border with electronics would be suspicious, but now people regularly travel with laptops, phones, portable consoles, and all sorts of other expensive electronics. Having another single item, not in it's retail packaging, would hardly bat an eye.

But, I will say that disclaimer that you "have to declare the item" is a bit iffy now. It used to be that the US forced everyone to submit paperwork with whatever they brought back with them from abroad with every entry. But, I think the Pandemic ended that. Now, it is very easy to simply leave without declaring anything. I would say that if you wanted to bring the thing back in it's retail packaging, it's worth taking the time to declare it, and just make sure you have a list of all the items you are bringing back. The customs agent may just wave you through once they are satisfied you are not reselling anything, but at least you know it is legit.