Welcome to the pepper fourm, we need more information, did you grow the plant from seed? Did you pick the plant up at a store? What kind of potting mix are you using? How large is the pot? Have you used fertlizer/how much? Did the plant spend a lot of time indoors? If so when did it go outdoors? How often do you water. What zone are you in?

I see you provided some of the information in another thread. If you put the plant outside without hardening it off then it's most likely sunburn. That's what it looks like. Some plants burn the way yours looks, others turn white, while some turn silver, I've had all three happen to me before.

Plant

Carolina reaper 12 inches tall

Potting mix

60 percent potting soil with 9month fertilizer 20 percent mushroom compose 20 percent peat

Pot is 15 inches round and 15 deep

Indoor a week to acculmate then outdoor due to issue that arises.

Day time temps here in rockford illinois 65 to 70 degrees

Night time high 40s low 50s anything under 50 I bring them in.

Fertilized when transplanted a week ago have not since fertilized

This begin indoors shortly after I got the plant from chilliplants.com where at my house they would get 3 to 4 hours of sun indoors. I moved them outdoor and treat roots with organic seaweed fertilizer like,instruction said to. I was watering them every morning and they got worse and read to let them dry up so I am which seems to be helping but no cure.

I read could be magnesium deficiency?, I also found other things it could be so I don't know.

Don't start throwing a bunch of nutrients at the plants. It looks more like a hardening off problem. It sounds like you have plenty of nutrients in your plants already. I planted my plants three months ago and just yesterday was the first time I gave them any extra fertilizer. My Carolina Reapers are 20" tall and putting out pods already.

Sunburn. Those leaves affected won't heal but new ones won't be affected and will be able to stand full sun just fine. The plant will survive and thrive just fine. It's a hardening off problem. Don't worry it happens to the best of us.

Sunburn doesn't make sense to me because this started indoor where they only received 3 to 4 hours of direct sun light.. New growth has same thing happening to it.. Leaves are yellowing now..

maybe a couple more photos and a photo of the entire plant.

Also, how often/when do you water? What kind of soil are you using?

First photo the plant looks a bit yellow but that could just be the lighting. It looks like you used the flash on the camera. The second plant looks good.

That is exactly what it looks like

Yeah nasty sunburn, but the plants will bounce back. My very first year growing peppers, I fried all the leaves on one plant before I knew better and it still survived and produced peppers. And as you can see I still accidentally burn them to this day.

So they don't need direct sun light or just limited hours... Why does sun burn happen?

Going from indoor to outdoor if you use lights or sun through the window is still filtered. The sun is too intense and just placing them out they get burned. If your zone permitted and you started with the sun then your plants would already be used to the sun thus no sunburn. Most bigbox and nurseries do the hardening off process some don't. Also if you have them outside then bring in for a few weeks then put them back out the leaves could burn as mine did.

I constructed a screen box to harden off plants, before then I used shade from a large tree, which I no longer have.

Search this fourm for hardening off and you can read more about it.

Do the bottom leaves always look a lighter shade of green.. Or even yellow?

Most always the older bottom leaves fall off, the newer larger leaves block the sun and the plant puts more energy to growth and pepper production at the top most part of the plant. I would only worry if the bottom and top leaves were yellowing and falling off the plant at the same time.