From what I’ve read, there are still parts of Mars generating a magnetic field, just not in the same way as here on Earth. There also seems to be a possibility that Mars could eventually have a magnetosphere again in the future under certain circumstances.
I think wed have detected a functioning magnetosphere already, though maybe remnants of it still exist.
My understanding was our magnetosphere was related to the rotating iron core of the earth
From what I’ve read, there are still parts of Mars generating a magnetic field, just not in the same way as here on Earth. There also seems to be a possibility that Mars could eventually have a magnetosphere again in the future under certain circumstances.
https://en.wikipedia.org/wiki/Magnetic_field_of_Mars