Emulator

uh that looks exactly the same to me.

It's not. Look at the spacing between the menus and toolbar icons (Qt Dolphin vs Qt VirtualBox).
Or the check marks in the check boxes and the arrows in the drop-down lists.

I also checked RPCS3, they are using Qt 5.8 and no issues there either.

You probably think these are non-issues, but it's a pity that under wxWidgets everything looked
perfectly and then the new Qt GUI makes everything pixelated and too large.

I have a HiDPI screen and will verify it. I know the effect that you're talking about and if it's happening I will accept this.

JMC4789 << Thanks for trying to solve this issue:) Did you have the time to confirm this?

In order to fix this I actually had to rework all of RPCS3's original Qt layout (which was created by me anyway).

I personally use my TV sometimes which is configured to 150% scaling in windows.
That way you can clearly see many issues with dpi scaling.

Same issue can be seen on Citra as well.

I might take a look sometime soon. Qt's highdpi scaling interfered with the render window if I recall correctly, so that might need some work in case it happens.

But I personally would start with preparing the settings dialog's layout first, regardless of scaling, and work myself through all the widgets from there until I can enable the scaling properly.

I will look a bit different because there won't be custom placed widgets anymore (if they even exist). At least until someone goes through the trouble of properly setting them up with screen properties in mind (which is unnecessary in my opinion).

As closing words I just want to mention that I fixed yet another scaling bug only a few days ago.

All the issues I mentioned for Dolphin, are fixed in RPCS3, so I guess it should be easier for you to fix those...
I also revisited RPCS3 and found a few minor issues, maybe you can look into those as well:
https://github.com/RPCS3/rpcs3/issues/3580

Appreciate your work, these kind of UI issues are usually overlooked and sometimes never fixed.