I did not install a microcode manually. This comes automatically with new kernels. The microcode is maintained in the kernel and further developed as I read it in various articles in the press.
By me:
picnerd@picnerd ~ $ dmesg | grep -i microcode
[ 0.000000] microcode: microcode updated early to revision 0xb4, date = 2019-04-01
[ 1.255009] microcode: sig=0x906eb, pf=0x2, revision=0xb4
[ 1.255146] microcode: Microcode Update Driver: v2.2.
picnerd@picnerd ~ $
Probably it will not be displayed in your virtual machine because only the most necessary is virtualized to display the hardware level. The virtualized system has no direct access to your hardware.
Greetings