What does the Question Mark Folder mean?

Diam_ wrote:

But why does it even come up is the question.

That is a question which may be difficult to answer. If you used Disk Utility, and either reinstalled macOS, or restored from Time Machine, you do have the option of contacting Support with the link on the referenced Support Article.

Have you ever attempted to use Safe Mode? That may clear some faulty cache files which exist on your HD.

If you are familiar with Etrecheck, you could download/install/run that application, and post the report to this thread.

If your Mac starts up to a question mark - Apple Support explains your options.

It comes up when it can't find the Bootable drive set in Firmware to Boot from.

This can be PRAM Battery problems, PRAM corruption problems, drive being set to a non-existent drive, Drive corruption, no bootable OS found on drive, etc.