I am having issues getting two Dell monitors working with the USB-C MST (Multi-Stream Transport) function? The monitors are a U2722DE and a U2722D. The U2722DE is connecting (via DP Output) to the U2722D (DP Input) using the DisplayPort cable that came with the U2722DE monitor. The laptop is connected to the U2722DE monitor using the USB-C to C cable that came with monitor connected to the Thunderbolt 4 port on the laptop. There is no issue with laptop connecting to the U2722DE monitor, but the U2722D monitor says no DP cable is connected. MST is enabled on the U2722DE.

If I run an HDMI cable directly from the laptop to the U2722D monitor the laptop happily runs both monitors.

The laptop is a HP EliteBook 840 Aero G8 supporting two Thunderbolt 4 with USB4 Type-C 40 Gbps signaling rate (USB Power Delivery, DisplayPort 1.4) and HDMI.