Comment 14 for bug 1882890

Same problem here on Ubuntu 20.04 in a Dell Latitude E7470 with a Core i5-6300U. The machine hangs on boot. I can not even reboot the machine using the alt-prtsc-b. It was completely frozen. Only a long press on the power button would work. My workaround was to boot into recovery mode (maybe you a need an older kernel for that) and do a

apt --purge remove intel-microcode

The purging process rebuilds initramfs. After that I could reboot again.

Here is the output asked above.

pjssilva@trinity:~$ dmesg | grep microcode
[ 0.102417] SRBDS: Vulnerable: No microcode
[ 0.578849] microcode: sig=0x406e3, pf=0x80, revision=0xcc
[ 0.578971] microcode: Microcode Update Driver: v2.2.

This looks like a serious bug. Maybe pull out the update from the repositories until a solution is found?