I personally don't understand the point of still clinging on to mask well into 2024 but definitely from my most recent visit to Seoul, masks are extremely low and it was relaxing enough to walk around. Can't say the same for Tokyo though. Anyway, just want to say that Seoul is an amazing city and we always have a great time there.
Cold cases increase due to daily temperature differences before last week and the aftermath of fine dust inflow from China. Unfortunately, Seoul and near area's geographical characteristics often suffer from westerly winds in even early summer, so if polluted and bad air from China flows through the sea, it will act as a filter.