I tried to separate these plates with a brick separator, but all the sides broke off instead😭

If memory serves that particular brown in recent manufacturing from Lego was known by the public over some time to have embrittlement issues, so probably not something you did to it, but something as of now that Lego has fixed on their end if you pick up that brown from a current set or from their stores.

Yup. And afaik Lego will replace the broken pieces for free.
- they will? is there a form to fill out or something?
The old brown from the 90s had the same problem; I've broken several while dismantling old used LEGO and it sucks. A lot of them were used in the old, kickass Pirate ships.
- I have the complete shell of that pirate ship and the body is still very strong. All the brown accessories however (muskets, barrels, etc) turned to dust long ago.
The new lime green joints?

Box of shame or hall of Fame, you decide where to hang this bricks frame

Someone keep this Lego poem going.

Damn. First time I've seen a separator both fail and succeed simultaneously.

true lol

Get the torch. It can’t be stuck if it’s liquid

Muddy stream piece.

You found a worthy contender to fight a Nokia.

There are such things as brick separators?! Why hasn't anyone told me, my fingernails could have been spared such anguish.

They've put them in every full set I've received the past several years. So I have a bunch of them now.
Yep, have existed for decades lol
- I remember one of my elementary school teachers back in the 90s having a few, but even as a kid who got a lot of Lego sets I somehow never got one of my own
  
  Until a couple of years ago, I'm now a grown ass adult, and my wife and I have been on a bit of a Lego kit, and just about every set we get seems to have one now.
  
  So somewhere along the line Lego seems to have pivoted towards including more brick separators. I'm certainly not angry about that, but I definitely get how it could seem to some people that they're a mysterious new invention.

The old "Reddish Brown" as of three or more years ago is know to be brittle. LEGO has changed to formula since which apparently fixed that.

Apart from your problem of getting the remains out, just contact LEGO support for free replacement parts, as this is a known and accepted issue. Keep the parts, though, if you ask for a larger number of parts, they might want the broken pieces back as proof (theoretically, I have nor heard of such a case personally).