I think it will pull through eventually. You can't go wrong with a 90% markdown. Those brown crispy leaves are too far gone and will never recover, but it should start generating a new top fairly soon. Things are happening underground, you just can't see it yet, but with a little more TLC, you will. Keep it watered with all the sun it wants.

I could be wrong, but your plant still appears to be in a pot, pretty sure I can see its rim.

Plant it, now, in a spot that receives some light shade at some point during the day, in rich, fertile soil. That probably means you need to dig over the area you choose to plant it in and add some composted manure or good garden compost, but choose a spot where there's enough room for it to get 3/4 feet tall and wide. Keep it well watered. Zone 10a is pushing it a bit,they do better in zone 9,but its worth a try. Do not use high nitrogen fertilizer, they're over sensitive to it. More information here, you'll need to copy and paste into your browser

https://www.gardeningknowhow.com/ornamental/flowers/peony/growing-hybrid-itoh-peonies.htm

I wish you luck with the Itoh Peony, Ben, but the info that I have is that they need cold winters almost as much as regular herbaceous Peonies. It's getting ready to go to sleep for the winter, but if you want it to wake up again, you'll need to put a bag of ice over its "bed" every night through December and January. That's how the few people that grow Peonies here in the Valley of the Sun manage them.

Thanks all!

Do you think it could be over-watered? Do they like to dry out? I have kept it just moist, without letting it dry out.

I know I am pushing it with the zone...but get this...I bought it at a Lowes near the ocean! Sunset Zone 24 haha!

I've read that some have had success with this kind of peony in 10a and 10b. Our nights dipped to 35 consistently last winter. Apparently that is enough of a chill to stimulate bloom. Either way, I am so jealous of my mother's ridiculously gorgeous peonies in Washington state that the $5 price tag was well worth it.

I'll plant it once this 100 degree heat wave passes this week and keep you all apprised on how it fares. :)

Oh, this is also the "Keiko" variety - those are the specific ones that can do well in zone 10. Kind of rare, hence the original $75 price tag for a 3 gallon!

Hmm...from what I can see, it is still listed for zones 4-8, no 10....
Well, I still wish you well with it, and am interested to see how it turns out! Just from my general plant experience, I would soak it thoroughly--don't worry about giving it "too much water" at any one time: overwatering comes from watering too often, or insufficient drainage, not giving it too much at one time--and letting the top 1/2 inch of soil dry out before watering again. I would give it a very light dose of water soluble, low nitrogen fertilizer, just to make sure that the neglect at Lowes didn't leave it with malnutrition. I wouldn't expect any improvement in appearance until it is ready to come out of dormancy in spring, but every week it can absorb sunlight through the remaining green surface will make the future growth stronger.

Thanks, Tug!

You're welcome, Ben!