Are you using SDDM (for Plasma), GDM (for Gnome and Budgie), or LightDM (MATE) as your login manager? If you're not sure then you are probably using the default SDDM for Plasma, the default GDM for Gnome/Budgie, or the default LightDM for MATE.

From the flashing cursor hit CTRL + ALT + F3 to get to a different TTY, login, and then type in the relevant command to restart the login manager:
SDDM:

sudo systemctl restart sddm

GDM:

sudo systemctl restart gdm

LightDM:

sudo systemctl restart lightdm

If this brings up the login manager and you are able to login please comment back, I may have some dev packages for you to test that may resolve the issue and cause the login manager to not fail on startup (and have to be restarted).

    ReillyBrogan Since I posted this issue, every week I’ve been trying to solve this by just installing Nvidia drivers (hoping they’ve been fixed), ending up with an unrecoverable system, then needing to reinstall my OS afterwards (I always back up my data on an external drive beforehand of course). Yesterday I hadn’t seen your comment and I again, like every weekend, installed Nvidia drivers and ended up with a broken system. I couldn’t be bothered to re-install it yesterday, so I postponed until today.

    I decided today to look at the forums and noticed your comment. When I re-installed before with Nvidia drivers, I used to install the OS, reboot, update the system, then install Nvidia drivers. When I install the Nvidia drivers on the weekend, I always do a full system update before. Today, however, when I was re-installing my system, I forgot to update and immediately downloaded Nvidia drivers. My system then booted perfectly fine. I then did a system update, rebooted, and my system works fine.

    I am unable to test your recommendation (I know that I am using lightdm on Budgie btw), since my system works fine now with Nvidia drivers. It seems all that I needed to do was to install the drivers before updating. If my system breaks later on, I’ll let you know.

        It seems I was very wrong. I now remember why I used to install Nvidia drivers after an update. Nvidia drivers are not properly installed the way I did it, and they need to be installed again. I only just realised this, and once I noticed and remembered this, I installed Nvidia drivers. They do not work. I also, as usual, am unable to go into a tty with the keyboard.

        However, when I go into clr boot manager at boot, I am able to switch kernels. When I switch from kernel 5.15 to 5.13, I am able to get into a tty. Restarting lightdm doesn’t fix the issue, however this at least allows me to recover my system by uninstalling Nvidia drivers and then restarting lightdm.

        9 days later

        DragonEggBedrockBreaking This may be fixed by a systemd update actually. Can you run the following in a bash shell in order to install some test packages?

        installed=($(eopkg li | grep systemd | awk '{print  $1 "|"}'))
to_install="sudo eopkg it "
for i in "systemd" "systemd-32bit" "systemd-32bit-dbginfo" "systemd-32bit-devel" "systemd-dbginfo" "systemd-devel" ; do
  if [[ " ${installed[*]} " =~ " ${i}| " ]]; then
    to_install="$to_install https://solus.reillybrogan.com:8443/systemd-250/$i-250.7-105-1-x86_64.eopkg"
  fi
done
eval $to_install

            ReillyBrogan I am not able to using keyboard shortcuts. I can access a command line by appending init=/bin/bash to the clr boot manager arguments, then from there I can uninstall nvidia drivers. Systemctl restart lightdm fails.

              @DragonEggBedrockBreaking I prepared some patched packages that may help. Can you please fully update your system, and then before rebooting run the following?

              to_install="sudo eopkg it "
installed=($(eopkg li | grep linux-current | awk '{print  $1 "|"}'))
for i in "linux-current" "linux-current-headers" "linux-current-dbginfo"  ; do
  if [[ " ${installed[*]} " =~ " ${i}| " ]]; then
    to_install="$to_install https://solus.reillybrogan.com:8443/kernel-5.15.50-patched/$i-5.15.50-217-1-x86_64.eopkg"
  fi
done
installed=($(eopkg li | grep nvidia-glx-driver | awk '{print  $1 "|"}'))
for i in "nvidia-glx-driver-32bit" "nvidia-glx-driver-common" "nvidia-glx-driver-current" "nvidia-glx-driver-modaliases" ; do
  if [[ " ${installed[*]} " =~ " ${i}| " ]]; then
    to_install="$to_install https://solus.reillybrogan.com:8443/kernel-5.15.50-patched/$i-515.57-431-1-x86_64.eopkg"
  fi
done
eval $to_install

              This will install my patched linux-current packages as well as replacement versions of the nvidia-glx-driver packages built against that kernel. I didn't rebuild any other kernel modules so if you have anything like virtualbox-current installed expect that to stop working. Note also that I didn't build a LTS package for the Nvidia driver, so if you use LTS that might be an issue too.

              If that doesn't work I have another idea we can try.

                After you "fix" the system by reverting it to previous packages can you retrieve the boot logs of the previous boot and upload them here? You should be able to access them with sudo journalctl -b1 --no-pager (the number after -b means how many boots ago where 0 is the current boot and 1 is the previous one. You may need to adjust till you find the right value which should have the correct kernel version listed in the first few lines).

                  WetGeek Yes. I’ve reinstalled solus at least a dozen times since making this post. I’ve also had to reinstall other distributions countless times, ranging from easier options like mint and fedora, to more time consuming options like arch and void.

                    Could you try installing the 470 driver by following the directions in the other post? At the very least that'll help narrow down the issue.

                      It's unfortunate that we don't know what version of the kernel and drivers you were on before. That makes it difficult to identify what exactly broke your system, was it a bug in a newer kernel or something to do with the driver update? Or something else unrelated. Do you happen to know roughly when the last time you updated your system was before it broke?

                        I mean when was the last time you updated your system and it worked afterwards. If you know that then perhaps we can estimate which kernel/driver version was the last working version for you.