Folder with the Question Mark on the MacBook Pro A1708 and what you should try first

This video shows you the procedure that give you the possibility to force the boot process and verify whether your SSD is malfunctioning or not.
It was shot to illustrate the solution given by me on iFixit.
Direct link to the discussion is https://www.ifixit.com/Answers/View/6....
Despite what Dan says you don't need any other disks and your drive most probably is fine. It will pass all possible tests once you boot from it, well unless it is indeed dead.

How would you know whether your SSD is dead or not?
It is quite simple to figure out too.
When you see the folder with the question mark just do a forced reboot by pressing Control+Option+Shift+Power Button key combo one press, NO holding, and next press Option key during the boot-up.
If you don't see any drives there, where you normally see the list of drives to boot from  - then your SSD is out of order and only then all what Dan said will be valid to continue the investigation.

But if you see your system drive there in the list of drives to boot from, then your drive is most probably OK. Just choose the drive and boot from it. Till the next shutdown you'll see no folder with the question mark again. Even if you have to restart, your A1708 will boot up normally.

After the shutdown, next time you'll start the system you will see the folder with the question mark again, so just reboot with the Control+Option+Shift+Power Button key combo (one press, NO holding) and your Macbook Pro A1708 will boot-up normally without the need for you to choose which drive to boot from.

So the regular key combo for the SMC reset (Control+Option+Shift+Power Button) works in this case too. One press but no holding it for 10 seconds. So just as I've suspected you don't need to press +Command to get what I am showing here even though that Control+Option+Shift+Command+Power Button key combo, showed in this video, will work too without any hassles.

Is this a working solution?
Yes, absolutely.
It helped in several cases, most of those cases were with A1708 which have a replacement 2242 / 2232 SSD drives on the HFHK N-1708A adapter. I will not speculate on the exact source of the problem, but if it is not a problem per se, who cares? Do you need your computer to compute or do you need to spend time on the search for how to make a bootup disk without the working computer?

As a usual post scriptum: Do not forget about making regular backups of important data and use drive monitoring software no matter which drive you are using. Be safe.