I installed 3 smart switches on one side of our entry by connecting each to the white bundle of neutral wires at the back of the box. Pretty simple and they all work fine. There are 3 more switches I want to replace, but what should be the neutral wire bundle has 2 black wires. Do I have the necessary neutral wires for the smart switches?[![enter image description here]] the 3 way on the left connects with the 3 way I just replaced in the other box. I added a drawing to make things clearer. The 2 black wires in the white bundle lead in and out of the box and are from the cables that include the red wires bottom left and top right.
It's hard to believe there are no neutral wires in that box. It's possible they used black wires for neutrals but I doubt it. Most likely those are switch loops where they used white wires as hots. The best way to find out is to get a multimeter and measure that black/white bundle against ground. If you get 120v you know it's hot.
There are many smart dimmers that don't require a neutral wire. Although they are requiring it now for many devices. And the NEC now requires a neutral wire in switch boxes for this very reason.