A.E.D. wrote:
Further Questions: 1. Do you know what could have caused this malfunction? Or what the usual cause is?
Try a PRAM Reset. Sometimes a Mac will get confused as to which boot option it should be doing and a PRAM Reset will remove any boot options stored in the NVRAM so the laptop will need to search for a bootable volume (hopefully the internal drive).
2) If I were to erase the Mac completely, would this also solve the issue? Or would I still not be able to get to the login screen due to this drive issue?
If you erase the Mac, then you will destroy all the data on the SSD which has not backed up.
If you want to perform a clean install of macOS, then you will need to boot into a macOS 10.13+ installer since a third party NVMe SSD is installed in the laptop. Since the SSD icon is showing up as orange I believe your laptop has an OWC SSD which needs a firmware update in order to work with macOS 10.14+ (the orange icon is a sign which I've only seen under these conditions). This means you either need to attempt to boot into Recovery Mode using Command + R to see if it will boot into installer for the currently installed OS, but unfortunately some Macs will only boot into the oldest version of macOS regardless of the keys used which seems to be the case with your laptop since your screenshots show a pre-macOS 10.13 OS in Recovery Mode.
Another option for a clean install is to create and use a bootable macOS 10.13 USB installer if you have access to another Mac able to run macOS 10.13. If you cannot access a macOS 10.13 installer, then you will need to install macOS to an external drive and upgrade the external drive to macOS 10.13 so that you can run the SSD firmware updater and so you create a macOS 10.13 USB installer so you can perform a clean install of macOS to the internal SSD (macOS 10.14 if the SSD's firmware is updated).
Personally I believe you should try the steps I outlined in my previous post to attempt to reset the password or to create a new admin user account assuming you can boot into Single User Mode so that you can reset your original account password. The first option requires Filevault to be enabled while the second option cannot have Filevault enabled since we need to access the data on the drive to trick macOS into running Setup Assistant again. Both of these options will leave all your data, apps, and settings intact if successful.
Edit: Here is a link to the instructions for performing a PRAM Reset (hold the reset for at least three chimes if possible):
Reset NVRAM or PRAM on your Mac - Apple Support