Why does Ubuntu slow down on a virtual machine?

Question

linux

Installed ubuntu via virtualbox. Delivered additions for guest OS. I want to use it permanently, but it slows down. Strong friezes, especially in firefox. I have a fairly powerful computer. Under the virtual machine allocated 20 GB of RAM. In theory, everything should fly in general, but no.
Lowering the resolution to full hd helps to reduce lags (I have a 4k screen), but sitting and sticking into a meager window is such entertainment.

Ubuntu is also worth the second system, but I need a virtual machine. I don’t understand, maybe virtual machines should work this way, but even on a weak aimak with 5k resolution, I launched Windows through parallel and everything flew without problems. And here is some kind of ambush.

Answer 1

Is vt-d/vt-x enabled in bios?

Answer 2

You start, as I understand it, from Windows. There, in the parameters of the virtual machine in the "Graphics" section, there is an item like "Hardware acceleration", so you need to enable it. (I write the names from memory)
If you are under Linux, then just put Gnome Boxes and that's it. No optimization, nothing like that, everything works great out of the box. Minimum hemorrhoids and maximum profit if Linux is on the virtual machine.