my suggestion would be to save everything off PC you want to keep and do a full reset.
one of the processes that can be broken by Critical process died is the login process, so that would explain your lack of a user. Not a lot you can do from a temp profile Guest account.
Does it show the login screen or just take you to desktop?
if you can get login screen
open the power button on bottom right of screen
while holding left shift, click restart button
this loads into windows repair
If the login screen doesn't show, you will need to use an installer to boot into same menu
On another PC, download the
Windows 10 media creation tool and use it to make a win 10 installer on USB
boot from installer, on 2nd screen after languages, choose repair this pc, not install
this takes you ro the windows repair menu mentioned above
how to save info off PC
choose troubleshoot
choose advanced
choose command prompt
type
notepad and press enter
in notepad, select file>open
Use file explorer to copy any files you need to save to USB or hdd
ONce you saved everything off PC, you can either do a reset or a clean install. Since you been getting critical process died BSOD, it might be faster and safer for you to clean install. Both will mean you need to reinstall all programs again. CLean installs fail less often than resets in my experience
Fresh install
boot from installer
follow this guide:
https://forums.tomshardware.com/faq/how-to-do-a-clean-installation-of-windows-10.3170366/
when you reach the screen asking for licence, click "I don't have a key" and win 10 will continue to install and reactivate once finished