You guys! My box of old #cables paid off! I bought an old optiplex 7010 as media server and could not get an image via displayport. The monitor triggered but nothing showed up. After reading this post: https://www.dell.com/community/en/conversations/optiplex-desktops/7010-black-screen-on-boot-resolved/647f8196f4ccf8a8de04de2d
I headed to the cellar, pulled out an old monitor with #VGA input and a VGA cable burried deep, deep in the lower strata of my cable junk and voila, it worked.
I will never throw away any cables after this!