Zen is a wonderful name! Welcome to you.
Temperature is very important. The temperature you keep the baby, and maintaining the temperature of the formula during feeding. To help maintain temperature of formula, I set the container of formula in a pot if water i simmer. Using a thermometer is very important. Cooler temperature leads to slower and poorer digestion , both of baby and of food. Cooler Temps cause the baby to burn more calories as well. Also can cause slight yeast or bacteria overgrowth, making them burn more calories while fighting a hidden infection. Its good to get them checked by an avain veterinarian, to swab and gram stain cloacal, cloanaenal and possibly culture. Possibly blood work. Its common to have issues while hand raising .
Fir older babies you have to thicken the formula slightly. That increases tge calories in the same serving size.
Because we have so many people come here with unweaned babies, I have done a lot of reading research. Most often failures to thrive are linked with temperature, and minor untreated infections, usually of the crop.
The one picture, I think I see a pretty watery poop, this can be from infection, or feeding to thin formula ..
Hopefully you've read up on weaning by abundance. After the morning feed, offer lots of veggies chopped up to pea size, offer soaked pellets. This is when they are best likely to explore and try new foods. When they have a full crop they feel more confident in try foods.
You might also need to add low perches, and a visual retreat. To lesson stress. Young burds need more physical contact, and interaction time. This actually promotes confidence and independence later as an adult. You need to answer every contact call, abd dint leave them begging fir attention. Your species would spend a year with parents, getting an occasional comfort feeding, and learning to forage, being protected and supported.
Yes its ok to feed peppers. Generally fir young parrots every thing should be chopped up to little pieces. Yes start offering everything from the parrot safe foods list! Don't forget tge leafy greens, romaine, bok choy, Swiss chard, dandelion greens, probably chopped or mincing. Soaked and cooked legume, lentils. They are programed to explore and learn from parents, while still receiving feeding.
A lot of care and thought needs to be put into babies pre, during, and post weaning. Its a very critical time in their lives , and you can prevent behavior issues, or cause them during this crucial time.
This is truly a great article. I wish it want titled stress in parrots, because it applies to all parrots. She even mentions the behavior problems caused by forced or early weaning.
https://lafeber.com/pet-birds/stress-reduction-for-parrot-companions/
This is great article on chop. Its a perfect way and size to introduce to your baby. Your baby might benefit from feeding a spoonful a day of Greek yogurt with Acidophilus, and lactobacilli listed in the live cultures, no artificial sweetners.
http://lovinglifefromscratch.blogspot.com/2013/07/chop-all-things-good-for-birdie.html?m=1
K snd H has a little panel cage warmer, or sweeter heater found on Amazon has radiant heat panel, smallest size us more than enough. Im a huge fan if rge sweeter heater, ive has one fir 20 years. It has more than paid fir itself and was critical in saving my sick bird.