[UniLogic Date-to-String or Numeric-to-String?]

I had the same problem few days ago, since I wanted to write date as string for future database use.
Just like Joe said, just import that function and call it. I made both strings 15 in lenght.

BR E.P.

[HDMI resolution on the PLC product]

Howdy.

Is there any progress regarding this or some sort of workaround?

BR E.P.

[One HMI (Unistream Lite) connection to TWO Unistream PLC]

At the same time? No.

But you can connect lets say 2 PLCs and modular panel acting as Unistream display to the same switch, (TL-SG605 for example). Then you set network settings for all devices, example bellow and you can access both PLC's from that panel. You can also save addresses, so you only switch from Connection 1 and Connection 2, no need to input everything again. Also connect PC with right network settings and you see all 3 devices. Be careful with giving switch internet access, if you do set passwords on all devices.

PLC 1: IP 192.168.1.85
PLC 2: IP 192.168.1.86
Panel: IP 192.168.1.87

Mask 255.255.255.0
Gateway 192.168.1.254

BR E.P.