"About this Mac" and "System Information" no longer working
When system information is unable to render the macOS version, I would connect a drive and back everything up as soon as you can or power off the mac and get troubleshooting help if you have files that are not backed up.

That out of the way, it’s probably something that can be worked, but why risk photos and other data that are not backed up when you know things are failing that should be rock solid.

Open terminal app (Applications / Utilities) and type:

sw_vers


That will report the last installation of your system software so you can take next steps. I would not install any updates or every restart if you have valuable data that might be able to be copied out of caution and not out of likelihood that you’re about to have more serious problems. Good luck and once you have those details - feel free to ask some follow on questions as you need more help.

Once you have a backup, you can boot to internet recovery and reinstall the version of MacOS you please. That will drop a new build of macos, all the tools and give you a start on what else might be broken or need looking in to with an install log that will have specific failure messages or your system will be healed.