We already have images of the Galaxy S21, we already have specifications of the S21 but so far we don't really know yet how the S21 differs from its predecessor. Largely because the specs are quite similar. However, one of the main changes Samsung wants to focus on is the fingerprint scanner.
At least that's what @UniverseIce believes. He or she thinks that the fingerprint scanner on the S21 is almost 2x larger. Moreover, its speed has improved. A short tap should be enough to successfully scan your fingerprint. Until now, fingerprint scanners in displays were slightly slower than physical scanners usually found on the rear.
Allegedly Samsung still uses an ultrasonic scanner that works by transmitting sound waves. Some other manufacturers use optical scanners that works with light. The ultrasonic scanners usually work a bit better because they do not suffer from wet or greasy fingers. The disadvantage, however, is that they are a bit more expensive and do not work with every screen protector, especially thicker glass screen protectors. Compared to optical scanners, they are also a bit slower, but Samsung seems to have solved that problem.
January 14th
According to the latest rumors, Samsung will announce the Galaxy S21 on January 14, most likely along with the S21+ and S21 Ultra. This trio will have a new camera layout on the back, but are otherwise very similar on paper to the current generation of flagships. Although the faster fingerprint scanner may be one difference.