Changes in the sun’s magnetic field by changes in internal physics and plasma movement create sunspots (Or seem to...they’re a big mystery!). Lies or low number of sunspots less solar window & weakened field strength.
The sun is a dynamic place it only looks placid!
Sun spots are indication of the Suns mag field. Fewer means a lower mag field.
Not unlike a transformer with the Earths metal core being the transformer core. Sun and the Earth. Don’t the Suns mag field lines envelope the Earth.