VirtualBox Configuration Font is Small

• Host OS:Widows10
• Guest OS: XUbuntu 18.04
• Laptops: 15"
• External Display: 42" (4K)

VirtualBox

VirtualBox graphical user interface
Version 6.0.8 r130520 (Qt5.6.2)
Copyright © 2019 Oracle Corporation and/or its affiliates. All rights reserved.

When you open the VirtulBox Manager on a laptop, the VirtulBox Manager font is too small to be seen.

The laptop display settings are shown below.

In addition, the VirtualBox VM display setting is 100%, but the font is small.
After changing the display settings to 200%, the font size is now appropriate.

Connect to External Display

When you open the VirtulBox manager on an external display, the font size of the VirtulBox manager is appropriate.

Also, the VirtualBox VM display setting is 100%, and the font is the right size.

How do I change the VirtualBox manager font to the appropriate size when I display it on my laptop?
Also, how do I automatically change the VirtualBox VM display settings when I switch displays?
I want to make sure that the font size is appropriate without manually changing the Display Settings.