I don’t know if this is the issue, but I suspect it is the antialias option, in bash I have it set in my .bashrc as export MNE_3D_OPTION_ANTIALIAS=false
Since you are on windows I dont’ know how to set this, but you might put this at the top of your script before the vizualization. And I think it has to be the string ‘false’ versus the boolean False.
import os
os.environ['MNE_3D_OPTION_ANTIALIAS']='false'
stc.plot(....)