Joanna, cut the brown spot off, seal it with wood glue or cinnamon powder and wait. Your mix may be too wet.

Marie

If the branch suddenly turn yellow like that is a sign of a tap root has been rotten. Not sure when you took that photo, like Marie said your mix hold too much water and possible for too long. Pull the plant out and inspect the roots too.

Thanks for advice, I will try cut and hopefully my plant will be OK .and pictures I made today

if you cut, sprinkle cut w cinnamon or sulphur and let it hang dry a few days before you repot in a mix that has very FAST drainage … ask if questions

So I have to buy special mix for succulent s ? Now I have combination of sand and soil

Sand and soil isn't good for adeniums, that may be the reason why the problem occurred in the first place. You can't buy a ready mixed mix that's ok for adeniums. Easiest is half c/s mix, half perlite, there are many other combos using grit and other ingredients but please don't use sand, most are way too fine they clog air spaces and stay wet. Soil is assumed to be garden soil which is also not recommended for adeniums or any other house plant really, its for garden plants.

The pic has hopefully identified the problem, this time...... but if you post a pic again, pls check that it's in focus as this one definitely isn't :-)

What is that green patch below the yellowing branch. If it is fungus, try to remove and spray the area with fungicide. If you haven't done so, you might want to check the root for rot. I have not seen an Adenium's branch die back like that naturally. It possibly to get the affect if the plant was in a dry stage for a long period of time.

I have no idea what it is... It's there since I bought it ...feels like a little flat hard stone stuck into the top

It looks like a sealant used on bonsai trees when a large branch is cut helps heal the scar.

Fresh roots should be round and somewhat stiff or firm to the touch. Color should be light yellow or cream. Sometime darker yellow or dirty yellow due to stay dry for too long. Regarless, the roots should not be mushy to the touch. Below is one of my plant when I unpot and discovered the rotting roots hidden inside the feeder roots ball. It seems like the outer roots ball of your plant are flat or hallowed. I tried to zoom in and the photo became distorted. If you can wash the roots ball and upload another photo that would be great. If you are sensitive to adenium's toxin, wear gloves and spray the roots ball.

What you need to do next are get a blade or sharp knife (one for garden use only) cut off all the rotten roots. If you have cinnamon or turmeric, sprinkle it where you have cut. Hang dry for about a week. Prepare a fresh fast drainage medium. Repot the plant and do not water for another week. Lite mist every two to three days is okay. Keep the plant in a shaded area. After 7 days, slowly move it back to full sun and water normal.

That rootball doesn't look right to me. Where are the main anchor roots, I see none at all? There should be fat roots with progressively thinner ones coming of the main ones. I'm suspecting that it has previously had major root surgery at some point and what we are left with is a secondary root system that's small for the plants size.

Any chance you can take some more pics from different angles in better light as in Shangs pic once you have cut off any dead or soft roots as advised? Sorry to be fussy. There may be something going on at the base of the caudex but it's not clear in your pic above. Does there appear to be any soft areas at the base of the caudex/ thick trunk?

Such a beautiful flower!