I can't tell if they are dry or rotted...

Many thanks. Would you advise to repot it and check the state of the roots?

That is most likely a good idea. It is either drying up or rotting. Roots will tell you. I have C. mesembryanthoides, and keep it under lights during winter and water about 1/2.5-3 weeks. But it looks better outsides. I have a feeling that it doesn't like indoors much, since it does loose bit more leaves, but not all. They just dry up to crisp. Photo below is from September, still outside. It is in very gritty mix.