Unexpected Kernel versions in two different x86_64 systems

[Ralf Mardorf]

On Thu, 23 Dec 2021 17:48:09 +0000, Ian Bruntlett wrote:
>ThinkPad T420: 5.11.0-43 kernel
>ThinkPad X230i: 5.4.0-91 kernel

Take a look at https://packages.ubuntu.com/focal-updates/linux-image :

linux-image-5.4.0-91-generic
    Signed kernel image generic
linux-image-5.4.0-91-generic-lpae
    Linux kernel image for version 5.4.0 on ARM (hard float) SMP
linux-image-5.4.0-91-lowlatency
    Signed kernel image lowlatency

linux-image-unsigned-5.11.0-43-generic
    Linux kernel image for version 5.11.0 on 64 bit x86 SMP
linux-image-unsigned-5.11.0-43-generic-64k
    Linux kernel image for version 5.11.0 on ARMv8 SMP
linux-image-unsigned-5.11.0-43-lowlatency

Or at
https://wiki.ubuntu.com/Kernel/LTSEnablementStack#Ubuntu_20.04_LTS_-_Focal_Fossa
: "The Ubuntu LTS enablement (also called HWE or Hardware Enablement)
stacks provide newer kernel and X support for existing Ubuntu LTS
releases."

It has got nothing to do with the way you installed or updated Ubuntu.
You or somebody else manually installed at least one kernel, probably
from the above mentioned official repositories. IIRC you installed a
HWE kernel, due to a hardware issue.