Dual OS (win10/Ubuntu) boot problem

I have installed dual OS Win10/Ubuntu, but I have some boot problems. My computer has a Nvidia GPU with a high refresh rate (144Hz) monitor. The monitor has DP 1.4/HDMI 2.1/Type-C interfaces. I first used DP cable, but when I boot the grub does not appear and it enters Ubuntu directly. Then I also connected the monitor's HDMI to the VGA interface on the motherboard (via an adaptor). Now two cables are connected to the monitor and I can switch between DP and HDMI. When I reboot and switch the input to HDMI, the grub can appear in general, if I choose Windows the monitor does not show the graphical interface, but I believe it has entered the Windows OS since the keyboard light is on and the monitor is not really black but with a luminance background. When I reboot and switch the input to DP, the grub does not appear and it enters Ubuntu again. My questions are: 1. Why is GRUB not displayed when I use the DP interface, and Ubuntu starts automatically? 2. Why does GRUB show up when I use the HDMI interface, but the monitor does not show a graphical interface if I choose Windows? 3. What should I do to make the grub displayed if I use the DP interface (because it supports a high refresh rate) to allow me to choose which OS to start? Someone else told me this problem has something to do with the high refresh rate (144Hz) monitor. Thank you for any suggestions!