Replacing 2-prong outlet - existing wiring has two neutral wires, one hot?
First, the outlet is just a red herring; it is just an older style of outlet.
There’s more going on in this box than you know
Note the extra black wires that you haven’t discussed at all.
What’s actually happening is that one black-white pair is delivering power from supply. The other black-white pair is delivering power onward to another point-of-use.
The red is delivering power to this outlet, with the white as neutral.  That means one of (at least) two things:

The outlet is, or was, switched.  And the red wire is (or was) coming back from the switch to deliver switched-hot to the outlet.  Perhaps it’s been wired to bypass the switch and be permanently on.

The circuit is a Multi-wire branch circuit or MWBC, with this outlet receiving one 120V “leg” of the circuit, and the black onward wires are the other 120V “leg”.  However there’s at least one defect with this setup: in an MWBC you are not allowed to use a device to splice the shared neutral.  It must be pigtailed.


It’s normally allowed to use the 2 screws on a (non-tab-broken) outlet as a splice point.  However that is not allowed in MWBCs.
Fortunately, you don’t need to care.  Just use a red wire-nut to join the 2 existing white wires to a short pigtail, and connect that to the new outlet.