This sounds like a hardware issue, it's likely that the shutter wheel is damaged. If you have recently purchased the item, I'd recommend requesting a refund. I would not recommend attempting to repair an issue like this yourself unless you are okay with destroying the camera or really know what you’re doing.
You could try a factory reset the camera software ...
You appear to be seeking to maximize the amount of background blur. Factors that increase background blur are:
Distance to subject (closer)
Distance to background (farther)
Focal length (longer)
Aperture (larger opening; smaller F-number).
Sensor size in and of itself is not a factor. However, it influences focal length choice and working distances. ...