First, the second daisy chained monitor MUST have DP in or mDP in. The usage of DVI/HDMI/VGA in any form will not work.

Second, which specific P monitor model?

P2219HC. I connected the DP out to my old monitor through DP->HDMI cable. It sort of works but there is overscan on the second monitor - the edges of screen are outside

Which is one of the reasons that we only validate the usage of the Primary monitor DP out port to the Secondary monitor DP in port or mDP in port.

XPS 13-9365 2-in-1 left side Thunderbolt 3 (USB Type-C) out port --> P2219HC USB Type-C cable (C to C) --> Primary P2219HC USB Type-C in port (Menu- Display- MST On)

Primary P2219HC DP out port --> DP to DP cable --> Secondary monitor DP in port

-or-

Primary P2219HC DP out port --> DP to mDP cable --> Secondary monitor mDP in port

I will buy perhaps P2219H as an additional monitor. Also I am attaching my other PC to the HDMI port on the back of P2219HC and would like the monitor auto switch inputs. I could have sworn I saw the auto switch option at one time but now except for the USB-C, HDMI and DP the other options (Auto select, auto select for usb-c and reset) are all grayed out. How can I enable them? thanks

PC 1 --> P2219HC USB Type-C in
PC 2 --> P2219HC HDMI in

Both PC 1 and 2 are on. Disconnect PC 2 HDMI cable from the P2219HC. Press the Menu button. Go to Input Source. Can you change Auto select to On? If yes, exit the Menu. Reconnect the PC 2 HDMI cable to the P2219HC. Press the Menu button. Go to Input Source. What do you see?

Now I see 4 options: Auto (grayed out), USB-C, DP, HDMI (selected) - I tried turning off monitor and turning back on, pulled the power cord out and plugged back in - auto is still grayed out - the other options like auto for USB-C are no longer there

Honestly do not know what caused this. Read this if you want to exchange it.

Turn off MST option in your monitor. If MST is enabled, then Auto selection of input source is turned off. Let me know if that works for you too.