🛇- SSD Unbootable (in Recovery) & Seemingly Wiped Post-Mojave Update

Hi everyone,

Currently stumped and at my wits end, with no idea how to proceed. (Not at all tech savy, and even more confused after troubleshooting over the past 48hrs, with the help of Dr Google).

Background: 13" Macbook Pro Mid 2012 (running on Mojave 10.14.6 over the past few years; 500GB Crucial MX500 SSD, with ~400GB unused).

Issue: incessant (every 2 secs) pop-up re: " your system has run out of application memory", recently. Multiple PRAM & SMC resets, to no avail. Also decided to install a minor Mojave security update that had been sitting in my Updates for some time. Shutting down again, the computer has since failed to boot, giving a white screen with 🛇 (pics attached).

Currently: [1] PRAM & SMC resets + initial attempt to boot into Recovery (with SSD in situ)= all unsuccessful. [2] Inspected the SATA cable= nothing overt (previously replaced in 2019 & new cable manually insulated). [3] Placed SSD in an External Enclosure= able to boot into Recovery, but SSD appears completely wiped?! (see attached- full 500GB unused; no partitions/volumes/files). [4] Unable to boot into Safe Mode and Single User Mode states, "could not find APFS system volume handle" (attached).

Not sure where to go from here- when the SATA cable previously failed, I was at least able to use the SSD in an External Enclosure and get on with things, however even this isn't working this time around. I also don't have access to another Macbook (to create a bootable USB, or attempt to use Thunderbolt).

Queries:

[1] Any idea what might be going on (hardware vs software)?- ?SSD corruption (possibly after the security update); ?an issue with SATA cable; ?other (I've had a few issues recently with apps being unable/failing to update, incl my Brave web browser, as Mojave is no longer supported- could the cycle of attempting to update apps + subsequent failure to update, cause the above?)

[2] Is the data on my SSD gone for good, given that I'm not seeing any of my previous partitions/volumes/files in Recovery? The SSD Enclosure isn't being recognised when plugged into a Windows PC- any workaround to retrieve some of the data?

[3] Don't have a bootable USB/Installation CD- any way to actually get back into my laptop/boot up?

[4] If I opt to erase the SSD and reformat/repartition etc, how will I get the actual OS back on it?

[5] I do have a Time Machine backup from January- will I need to play around with the SSD (partitioning/formatting/etc) as in [4] above, if I opt to restore from here, or will the SSD automatically assume the settings from my Time Machine backup?

[6] Anything else I should be doing/checking?

Would greatly appreciate any help- thank you.