1. An HDMI to VGA adapter has been connected. However, the ThinkPad T570 still does not detect the other monitor. See Figure 1.
2. Finally, I found that I needed to select “Extend these displays” under “Multiple displays,” instead of the default “Duplicate these displays.” See Figure 2.
3. However, “Rearrange your displays” now shows two monitors, 1 and 2. Yet the VGA monitor only displays: “Check Signal Cable.” See Figure 3.
4. In Display settings, click box 2 (your VGA screen), scroll down to find: Multiple displays → Extend these displays. Then most importantly: ensure monitor 2 is selected, and change the resolution to: 1024×768 (Recommended). This was still ineffective.
5. I finally found the cause: the VGA monitor’s connection cable was not plugged in. The final result is as expected. See Figure 4.
6. I usually prefer to place monitor 2 on the left side of monitor 1 (the laptop). But now, clicking the bottom-right corner of monitor 1 feels like clicking the Win icon on monitor 2. Right-click the desktop → Display settings. Find the two boxes under “Rearrange your displays” (1 = laptop, 2 = VGA). Click and hold box 2, drag it directly to the left of box 1, and align their top and bottom edges completely (the system will show a light line to indicate alignment). Click Apply to save. Test: sliding the mouse outward from the bottom-right corner of screen 1 should only move along the bottom/right edge of screen 1, and it will not jump directly to screen 2.