My machine is a 2015 13" MB Pro.
A couple of days ago, out of the blue, while it was operating normally, suddenly it got the "Black screen with a folder icon blinking"
I got a new compatible SSD, fresh installed Catalina, and everything worked fine.
Then I proceeded to restore the system from a TM backup. The restore process went fine, and completed successfully.
The problem is that when the system boots, with the backup external drive removed, the bar in the logo screen loads really slow in the last 1/3, and then after it seemingly fully loads, it gets stuck there.
I have tried disk repair, which completed with no errors, I even tried to restore from an older backup, but the problem remains. Note, that new installations of the OS work fine.
Right now I have booted in verbose mode and the last lines are these:
ALF, old data swfs_pid_entry <ptr> updaterules_msg <ptr> updaterules_state <ptr> DK: AppleUserUSBHostHIDDevice-0x100000382 user server timeout DK: AppleUserUSBHostHIDDevice-0x100000385 user server timeout IOUSBHostInterface(0x100000385): matching deferred by IOUSBHostHIDDevice