Exactly the same problem, seems to be an issue with the NVIDIA driver update.
Troubleshooting (https://help.getsol.us/docs/user/troubleshooting/) helped me bring up the console:
Boot failure
If Solus partially boots, you can generally get to a TTY using Ctrl+Alt+F2 to login and be able to run commands just like using a terminal. This enables you to run some commands to identify or resolve the issue.
Then I followed the steps in the History and Software Rollback (https://help.getsol.us/docs/user/package-management/history-and-rollback/) to undo the update that broke my installation.
Booted up successfully.
I subsequently ran "Hardware Drivers" under "System Tools" on the menu which I people confusingly refer to as "DoFlicky" to make sure I was using the correct NVIDIA drivers.
I did not re-run the update yet, but at least it's working now and I know how to fix it if it breaks again.
It would be nice to not risk rendering the system unusable when running what looks like a minor update the system nags you to do. It happens very infrequently, but when there is a problem it winds up being a major PITA on a distro that otherwise consistently knocks it out of the park.
I suggest adding this problem to the known issue list and having some control in place, e.g. don't update the NVIDIA drivers if safe conditions haven't been met, or give a warning, or just auto-execute DoFlicky? Not sure what is possible.
Hope this helps.