What does "kernel:NMI watchdog: BUG: soft lockup" followed by other errors mean?

Seems like a bug in the updated kernel; but, this maybe related to your laptop's battery poor performance. This you can be more affirmative by checking ACPI(Advanced Configuration and Power Interface) modules.

When my kernel was updated, I restarted my system and started the new kernel---however it failed to load and the same error messages were sent to the terminal.

I reverted back to my old kernel usage, which is still working for me.

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Maybe,not sure but newer kernel modules might have some enhancements which are unable to be supported by the current power source. Like, it needs more power or something.

Also, my laptop's battery performance has declined severely and it needs to be replaced in my case.

EDIT: (based on Nikos Alexandris's comment)

You may consider replacing your charge source; it may have something to do with power management.