"Mac dual system Setup system default Boot system" solution

Workaround 1:

Press and hold the option key to enter the system Selection screen:

Use the left and RIGHT arrow keys to select the disk you want to set as the default startup,

Then press the Ctrl+enter key at the same time. You can set it as the default boot system.

Workaround 2:

After selecting the Mac system to enter,

Click System Preferences-----> Boot Disk-----> enter for example with interface:

First click on the lock image below. And then make the changes,

After selecting the system that you want to set as the default boot, click Start button again to take effect.

"Mac dual system Setup system default Boot system" solution