Hi Again,   Just wanted to update this thread as I’ve now resolved the issue.  I’ve updated my Dell bios (from Mar 3/23 version) and now the monitor is being detected and working properly from the HDMI port.  
Hi I purchased a new LG UL500-W external monitor a few months ago.  I connected it by HDMI and it worked fine until yesterday. Then, for no apparent reason it stopped being detected by Windows 11. I’ve upgraded everything I can think of, incl windows 11,  Intel drivers, Dell bios etc.  However, when I go to system>display>multiple displays>detect other display it says “we didn’t find another display” .  Based upon trial and error,  I discovered that by using the USB-C port with an HDMI adapter (monitor HDMI plugs into adapter which plugs into usb-c),  it will work.  However,  I   need my USB port for  other purposes so this is not a good solution.   Can anyone tell me how get this monitor working again with the HDMI port ?    thank you in advance !  
XPS 15 7590 Cannot Detect External Monitor with HDMI