Yes, I'm familiar with the phrase "potato-potato" (sometimes spelled "potahto-potahto"), which is often used to indicate that two things are essentially the same or interchangeable. It's a playful way of acknowledging a minor difference of pronunciation or spelling between two words, while also emphasizing that the difference doesn't really matter in the grand scheme of things. The phrase has been used in various contexts, including in popular songs and movies, and it's possible that it was used in the Wednesday series you mentioned.

Yes. It's a common expression, even though I don't think anyone in the world actually says, "poh-TAH-to." I could be wrong. ¿Europe?

I've heard it on TV and in films. I've never heard someone say it in real life.

Yes, it is actually a common phrase as someone said below.