Question sign after update to Catalina

If restarting from your Recovery partition (Command-R) didn't work, you'll need to boot from an external backup (clone), and erase and reformat your internal drive or try repairing it with Disk Utility.

If you have a bootable USB drive, yes, you could try that. You should never upgrade without a backup on an external drive. In fact, even if you don't upgrade, you should always maintain at least one full backup on an external drive. As this is becoming obvious, if something goes wrong with your internal drive or your Mac gets stolen, you lose all of your data.

You may have friend that has an external bootable drive or make an appointment at the Apple Genius Bar, they "may" be able to repair it for you.

Cloning software and TimeMachine are the two most common ways to backup your Mac to external drives. Some use both, I prefer using clones because unlike TimeMachine backups, they are bootable and the external drives only need to be large enough to hold the contents of your internal drive. Where as TimeMachine externals need to be around 3 times larger.

There is no way to solve this issue at user-end, there are many, many, many people with the same problem. Seems that Catalina update is corrupting the EFI chip of some devices when updating. If anyone got a different result please keep us updated.

I have the same issue too, i had to buy a new ssd, and this fixed the issue for A DAY, after this ITS BACK AGAIN TO THE QUESTION SIGN FOLDER AT EVERY BOOT OR TAKING A LEAP YEAR TO BOOT, i resolved to always PRESS X when i boot or better still might go back to MOJAVE

See the article https://support.apple.com/en-us/HT204323

The question mark means that your startup partition is not bootable.

The MOST ANNOYING PART IS IF YOU REMOVE YOUR HARD DRIVE AND CONNECT AS EXTERNAL, YOUR MAC WILL BOOT, like it did mine so weird