I think the S21 series probably are quite sensitive to the type of adapter you use. You might need to find a Hi-Res DAC headphone jack adapter. USB C to 3.5mm adapter Samsung | USB C to 3.5mm not working | Hi-Res DAC headphone jack | Vid ARN - YouTu...
My S21 Ultra has the same issue as yours. Max capacity is shown as 4855mAH.Max charge is approx 4500mAH. But i do notice one thing, the max charge to value changes from time to time.I am not tech savvy enough to determine if this result is accurate o...