It's not new; it's just something that you happen not to have come across before. It's a relatively commonplace technique, although technically tricky to pull off well, not least because each narrator needs to be interesting enough for the reader to spend time with. But books with multiple narrative viewpoints date back to at least The Woman in White by Wilkie Collins, published in 1859.

It’s not new but it’s more authors are writing this way, especially in mystery/thriller, because of the popularity of the “unreliable narrator” trope.

I used that technique on one of my early books. I couldn't think of a better way to tell the story. The feedback I got from readers was they really enjoyed the alternating POV. Especially when I would have both characters describe the same event. It gave them a richer overview of what was happening.

Not sure I'll use it again. All depends on the story. Sometimes it just works.

It’s not a new literary device by any means. Most authors who do alternating POVs do third person limited, though, not first. I think first person is difficult to pull off with multiple POVs as most authors end up inadvertently making different character voices sound the same when constantly writing “I” throughout a whole book. William Faulkner managed to do it very well in several books, though, most famously in As I Lay Dying.

This is an old device as has been pointed out. Wilkie Collins, Bram Stoker, and Dickens (Bleak House alternates onmiscient and first-person chapters).

My favorite example is Shaw's "An Unsocial Socialist" which concludes with a letter from the main character itemizing how the novel we just read is unfair and inaccurate.

It’s not new. I read a book written this way nearly 20 years ago. I hated it. I didn’t realize that was happening until the third chapter so I had to re-read to clear up confusion. Also the author wasn’t that skilled (IMHO) so he had to move back and forth in time to give each character’s reaction to events.

It's very common in the rom-com genre, I've noticed. You get one chapter from one protagonist and then the next from the other.

Omniscient and 3rd person are the most common perspectives in older and classical literature. For a long time editors were reluctant to publish books in 1st person because of custom and that is was difficult to pull off really well. That has changed in the modern era where nearly half of traditionally published books are 1st person.

The other part, switching character POVs has also become more popular. It too is harder to pull off really well. One of the drawbacks is you don't get as close to any single character and sometimes get stuck with chapters for characters you don't even like. There are a lot of people that don't like the Game of Thrones books just for this reason. I know people that read the series skipping whole chapters because they didn't like a specific character.

This will never not seem like fan fiction to me. Such a lazy way to write.

All the A Song of Ice and Fire/Game of Thrones books are like this.

It reads like fan fiction to me too. Especially the first book, Perfect Marriage.

Another old example is Brothers Karamazov, although it was a tad later. Dostoyevsky is a bit less rigid with the POVs but they’re definitely distinct enough