How can I enable "Render layers in parallel using many CPU cores" option from QGIS python console?
Use this:
from PyQt5.QtCore import QSettings, QThread
# parallel rendering
QSettings().setValue("/qgis/parallel_rendering", True)
for use max cores
from qgis.core import QgsApplication
threadcount = QThread.idealThreadCount()
QgsApplication.setMaxThreads(threadcount)
And extra for use OpenCL acceleration
QSettings().setValue("/core/OpenClEnabled", True)