hard drive – Blinking question mark folder icon after Ubuntu USB boot

A few days ago, I booted into Ubuntu from a USB drive on my late 2011 13” MacBook Pro. The computer has an SSD that was installed about 5 years ago to improve performance.

Yesterday, I turned my computer on, it booted normally, I logged in, startup programs opened up, and then it froze. I left it by itself for a while, came back, and it was still frozen. I restarted it, and got a blank screen with a blinking question mark in a folder icon.

I first tried rebooting it again, to no avail. I rebooted into recovery mode so that I could use Disk Utility to copy the computer’s drive into an external HDD. Disk Utility sees my internal drive, but when choosing Restore I get the following error message:

restore failed, could not validate source – error 254

I then tried booting into Ubuntu with the same flash drive, which worked, and ran

sudo fdisk -l

in the Ubuntu terminal, which again shows (among other things) my internal drive (it appears as /media/newhd). I then ran

sudo mkdir /media/newhd
sudo mount /dev/sdb1 /media/newhd

I again get an error message, this time it reads:

mount: /media/newhd: wrong fs type, bad option, bad superblock on /dev/sda, missing codepage or helper program, or other error

Where do I go from here? I could try Clonezilla, but my understanding is that it can be quite painful to use. I’ve also read the hard drive cable can become damaged with time, so I was considering buying a SATA to USB adapter and trying to access the internal SSD from another computer, so as to determine if the disk itself is still working. Is there anything else I can do?

I don’t recall there being anything super important on the computer, but I’d rather try more data recovery options before wiping everything and doing a clean install of some OS (of course, assuming the disk itself is not the problem).