Poor performance with Virtual Box on MacBook Pro 2017

The problem is Retina itself. If you use other monitor with other resolution (no retina) you'll see much better performance. I think it's an issue with OSX and Retina/HiDPI Resolutions.

Using the second monitor for VM definitely will improve performance.

Another workaround could be using a remote connection to VM.

I installed XRDP on Ubuntu VM on my MBP and using RDP client for access, no issues with performance.

Please check this link. There is another suggestion to use tool for Mac to use an additional range of screen resolution, so your VM instance can run smoothly on retina display

I know that this question is very old post, but just in case anyone still wondering how to fix/solve this issue...

The problem is on Mac's Retina display, as @Rubén Gómez García stated.

The fix(ish) for this problem is:

Firstly, make scale factor to 100%. This is MUST.

Then, in the Finder, go to Applications -> VirtualBox.app and choose Show Package Contents from the Finder context menu to see the contents of the app package. Continue to go to Contents -> Resources -> VirtualBoxVM.app.

Once you found VirtualBoxVm.app, then open context menu to get to the properties of VirtualBoxVM.app.

Then, under General, there is a checkbox called "Open in Low Resolution", you can disable HiDPI display by checking this. Don't worry, you won't notice the difference between HiDPI vs. Low Res. At least I didn't.

In my environment (Macbook Pro 13inch 2020 with 32GB RAM, Core i7 + Big sur 11.5.2), the performance was greatly improved by doing this setting, so I will leave it here as a reminder.

Feel free to correct/improve my answer.