After opencore iMac mid 2010 to macOS Monterey black screen

Hello I made opencore legacy patcher on my mid 2010 iMac and install macOS Monterey, but when I turn on my iMac I have only black screen. Sometimes when I don’t click anything in a while iMac turns asleep and when I turn it on again I have a login screen, but it sometimes takes 20 minutes to happen. Did somebody have similar issue ?