Mac mini M2 2023, one display works fine. Issues with adding a second one.

Using HMDI for primary display. When trying to add second display (Both are Dell monitors, U2419H) they both flash for a second, and go black, unable to stop/interrupt this cycle. Same if I use just the Thunderbolt connection to the second display (as the primary or only one). When both are connected and flashing, and I have the Displays window open, I see where it recognizes the second monitor, but the flash is so brief, that's all I can do is see that there are two monitors on the screen. Any ideas. First MAC ever, Apple fan, but for all the other devices so far.