The rule is against discriminating based on country of origin, not currency. While an EU citizen from a non-Euro country might prefer paying in their local currency, they should be able to choose to pay in Euros and get the same price as everyone else.

Disclaim: I'm American and I'm mostly guessing here,

I know that sometimes companies create multiple SKUs of products to get around certain restrictions. For example, if the Coca-Cola in Poland is only sold in Poland, and is different from what's sold in France (let's pretend your flag is on the can) - then they're technically "different products" and don't have to follow the same regulations.

I know the WD easy stores sold at best buy are best buy specific so that they don't have to price match them with competitors, even though what the competitors sell have identical internals.

That's just different shops having different prices. The price discrimination that is banned would be like a shop near a border charging different prices to locals and border shoppers.

What? Electronics, cars too?

You can also have constant regular price and just give different discounts.

Via the payment processor.