Somewhere in the range that your laptop will almost certainly never see even a single event, but a very large datacenter or colo will have multiple events a month.

There is a lot of disagreement on bitflips from ionizing radiation. They are unequivocally real, and unequivocally very rare. Even when they do happen, a large portion of the chip is dark a lot of the time, and a lot of the live data in the chip is simply thrown away and never used. (Think prefetching) Some bits, if flipped, will break something but will not corrupt the disk and the machine will be able to recover.

Nobody really knows for certain exactly how big of a problem they are and how often they happen- it's all statistics, and it depends on things like where on the globe your computer is, what your building is made of, and what phase of the solar cycle we are in. It even depends on workload. Anybody who claims to know for certain...