Need help for external display on iMac 2013 with sequoia 15.3

Hello The iMac works great thanks to OCLP. I have an external display (LG ergo 32) that I would like to add with mini display port to display port cable. The iMac sees it but I get a black screen. Been tinkering with nvram settings but nothing happens. And I have a BT keyboard and not sure I can reset SMC or NVRAM with it.

Any suggestions appreciated.

Thanks.