Attempting to kill init means that something tried to kill PID 1. That's... abnormal outside of a shutdown. But it can be normal during shutdown. So uhh... yeah: if it continues to be a problem then it needs to be reported and fixed by your distribution. What distribution are you using?
I see kernel panics at shutdown most often on Arch-based distros after updating system packages.
It sucks when it happens during shutdown but it's typically not going to cause other problems... except perhaps not automatically booting if you wanted to reboot instead of shutdown.
A kernel update, if it's done right, shouldn't cause a panic. But not every distro does updates right.
If you know the old version and the new version then it might be useful to reach out to the Mint community and see if they're aware of issues like that.
Not sure how you searched but I assume you didn't use or know apt? How do you install packages in the first place? Through GUI or Terminal?
EDIT: I assume you use the Linux Mint GUI package manager. I can't find how to do this too, would need to search more detailed but I don't have enough time for this now, need sleep, don't have enough sleep.
Yes this is a kernel panic which occurs when something goes terribly wrong inside the system. This could be anything from broken software to defective hardware. You should observe if this happens regurlarly.
You could look at the package that's mentioned in the first line in Synaptic. The error message says it can't find a file. Fürst thing is do is check if that fike is actually there.
I have no idea what those are, unless Linux Mint (at least the XFCE edition) has one of those installed by default, I'm pretty sure I don't have any of those installed.
Personally I'd be worried there's a transient disk issue. I'd ensure my backups are good and files aren't being silently corrupted. I assume you're on an NVME, they tend to fail instantly, but sometimes you'll get transient file errors beforehand (like not being able to open a system library). Look at something like debsums to start with maybe.
I'm not having the issue anymore, I'm not sure what fixed it though as I tried multiple things yesterday.
Also, I'm not using an NVME, I'm actually just using an old laptop hard drive with one of those hard drive cases that basically converts it into an external hard drive.
That type of error is usually indicative of hdd issue. I only mentioned NVMEs because they tend to fail all at once, without recovery options. Spining disks usually fail slower (but not always). Take a peek at smart info, maybe run a scan. My guess is the cord got jostled though tbh
As others said, check if it is a single case or if it repeats at the next shutdowns.
Anyway, the main question this brings to mind is: do you have a good backup of your system / data ?
I don't have a backup of the system because if something happens, I'm switching distros. But I do have both an external hard drive and Pcloud for cloud storage for some other things like game save files.