I bought a grafted avocado tree almost a month ago. You can see the state of it when I bought it in here. The seller said to transplant it directly into a big pot of at least 20-30cm. I did, water it, and realized that I did not mix enough perlite and it was extremely damp and wet all the time (for some reason I watered it again after a week). After letting it for two weeks and seeing it in a worse state daily, I decided to take it out, take also the potting mix and mix perlite in it. I also cleaned very well the roots, to take out the mix it came with (see pictures in previous link), by moving it inside water, and I read this is very bad for its roots. Too late for that now. Roots didn't seem rotted. I also tried untangling some of the roots so the plant of have a wider area to absorb nutrients.
I haven't watered it since, letting the soil dry. It's only a bit moist now, so all good. But it seems it's dying. Picture: Leaves are drying and curling up, also drooping, browning in color.
I live in a dry area, so the white spots are probably dry water droplets after spraying a bit to increase moisture on the leaves. The avocado plant is next to a window, and gets light all day, but it's not directly sun, but the reflection of the sun in the building in front. So I guess this shouldn't be a problem, but the opposite, it helps when transplanting to decrease the effects of transplant shock.
Is the pot too big, as stated in a question in this site? In here they say transplant shock is not dangerous for avocadoes?? In most sites they say transplant shock may be temporary (so only patience will give us an answer), or may cause them to die.
Update: 1st January 2023
Leaves kept browning and falling. I decided to repot it today to a smaller pot, and adding more perlite. I washed the roots and they seem extremely dark brown/black, but they are not "mushy", as a lot of places state when there is root rot. But I think the color (compared to the original when I first got the plant) is troublesome. I guess there is no saving for this plant, but I will keep trying.