Ubuntu 20.04 not booting after failed update and cannot access grub menu

I’m a relatively new Ubuntu/Linux user and am looking for some advice on how to potentially save an installation of Ubuntu 20.04 on a Dell Precision 3431. Ubuntu 18.04 came preinstalled on this machine. I updated immediately and its been running 20.04 fine ever since. Yesterday, a failed update appears to have resulted in an inability to boot - I get the Dell Splash screen but then a black screen with the white flashing underscore in the top left corner. I am not an expert Linux user but some research led me to try a bunch of stuff with mixed results. As of yet, I still can’t get the system to boot.

I attempted to boot into the grub menu by pressing F12 or DELETE while restarting the system. However, I cannot acccess the grub menu this way - I get a bunch of text flash by, from which I catch:

[FAILED] failed to start show Plymouth Boot Screen 

All other tests seem to pass. I understand that something is wrong with grub.

I tried to boot from a live usb and to repair grub that way. Not being able to access the grub menu is a bit of a problem but I found this https://szymonkrajewski.pl/how-to-boot-system-from-usb-using-grub/ tutorial which worked and allowed me to do so. I ran boot-repair, which apparently did fix some things, but the system will still not boot AND the failure to start show Plymouth Boot Screen persists. I am able to access the Grub BASH-like editor though by hitting escape while powering on.

I understand that it is also possible to rescue booting from the grub command line. I typed ls to identify available devices and tried booting using the following commands

set profile=(ls0,gpt2)/boot/grub
set root=(ls,gpt2)
insmod linux
insmod normal
normal

From here, I get the chance to boot in linux .The Ubuntu boot screen appears but then I get a BusyBox shell telling me:

(initramfs) Unable to find a medium containing a live file system. 

I’m increasingly accepting that I’ll just need to do a clean install but I’d like to try one more time to save those few files on desktop that I didn’t back up. Does anyone have any suggestions or advice?