The EVF brightness can be set to AUTO (Screen Setting - EVF Brightness). Did you perhaps switch that on ?
Also, did you perhaps switch Preview Exp./WB to one of the other two options, i.e. WB only or OFF ?
I am not sure if the reset restores these settings. Does the actual exposure match the histogram ?
If you set the shutter to 10”, (ten seconds) and try to capture an image, what happens?
p.s. Welcome to the forum.
p.p.s. If you have the shutter speed set too high, over 1/4000, only the electronic shutter will be available, — faster than 1/4000 is too fast for the mechanical shutter.