In theory, we built a space station orbiting Mercury like the ISS on Earth. Will the magnetosphere of Mercury similarly protect humans from this radiation (despite being close to the sun)?
No. Mercury's magnetosphere has 1% of the strength of that of Earth, and Mercury is about 2.6 times closer to the Sun. Even Mars' magnetic field is stronger despite not coming from Mars' core. So humans can't survive in Mercury's orbit on an ISS-like space station. A better idea would be to land a crew on the night side of Mercury since Mercury's days and nights are very long.