Here are the particular circumstances: I got the seedling in fall 2020 and I had it indoors until April 2021. Since then it was outside in a smaller pot. At the end of June I left for two months and at that time the plant was in a perfect state - green, fresh and obviously growing at the ends. When I came back late August 2021 I found what you see on the photo: the middle part of one of the branches was brown and the brown part is kind of spreading (I think). In the meantime I moved it into bigger pot (the one on the photo). I moved it without disturbing the soil and also noticed some roots have been on the periphery indicating the former pot was too small. I also sprayed it twice with antifungus and made sure it has enough water but also well drained.

Can you identify the problem and is there a cure?

Thanks. Stefan