The Galaxy Z Flip 6 might not have Samsung DeX, but it does have a better desktop mode. When you connect your Galaxy Z Flip 6 to an external display, you don't just get a mirrored screen. The Galaxy Z Flip 6 again misses out on Samsung DeX support, but it at least has a pretty decent desktop mode.
To connect a Samsung Galaxy Z Flip 6 to a monitor, use a USB-C to HDMI adapter. Plug it into your phone's USB-C port, then connect an HDMI cable from the adapter to your monitor. You can also use the "Smart View" feature on your phone to wirelessly mirror your screen to the monitor, ensuring both devices are on the same Wi-Fi network.
Make sure you are using a USB-C to HDMI adapter, not a USB-C to USB-C adapter.