Virtual Box and Ubuntu 20:04: Ubuntu for the secondary monitor behaves not correctly

I have in some laptops installed VirtualBox 6.1.28 r147628 (Qt5.6.2) where:

• The Hosts are MacOS (El Capitan) and Windows (7 and 10)
• The Guest is Ubuntu Desktop 20.04 for each Host.

The Guest Additions was installed through the .iso file. Therefore is possible:

• Share directories copy/paste between the Host and Guest
• Copy/paste between the Host and Guest

About the Display (Monitors). For each guest instance the configurations are:

Video Memory:  64MB
Monitor Count: 2
Scale Factor:  100%
Graphics Controller: VMSVGA

According with:

• What are differences between VBoxVGA, VMSVGA and VBoxSVGA in VirtualBox?
• 3.6. Display Settings

When Linux is the Guest, should VMSVGA be used . So I am assuming my current configuration is ok. I am able to get the 2 monitors configured, and based on extend. Furthermore was mandatory do the following:

1. In the login screen do clic in the Settings icon and not use wayland
2. Once logged go to Settings -> Displays -> Join Displays - the resolutions are based mostly according of the Host - it how reference

The problems/reasons of this post is again about the Display Monitors:

Problem 01: for any Host - when the Guest is running and applied the Host + F combination - I am able to see both monitors in full screen for each one. If I want return to the Host to do anything - does not matter if the Host uses one/multiple desktop(s) - practically the 90% of times the secondary virtual monitor disappears automatically - so is mandatory do the point #2 mentioned above. - How solve this?

Problem 02: In Windows 10 Host, exists two problems in the Guest- one the primary monitor has a small font. I did to the following:

• Settings -> Large Text - enabled
• Tweaks -> Fonts -> Scaling Factor from 1.25 (by default) to 2.00

But it improves something but is not perfect ... BTW - Tweaks is available because gnome-tweaks was installed (btw it was named gnome-tweak-tool before) - it due workspace configuration, more details here:

• Ubuntu does not isolate the apps in the secondary monitor through each workspace

Two the secondary monitor is really small. It is in the middle of the screen and has the size of a tablet. How fix these 2 problems?

Problem 03: In Windows 7 Host, in the secondary monitor (42/44 inches) I am able to see anything, for example a Terminal and Firefox opened. But is impossible do click in their links or/and resize/close icons (The fonts and icons are normal). To execute a link is mandatory do and keep press the left click and then press the Intro/Enter button. How fix this?

Extra Questions:

• Should I do something extra in VirtualBox? About its configuration?
• Should I install something extra in Linux? Such as I did do for gnome-tweaks? I have the impression that either something extra must be installed or something extra should be configured