Coming from windows, I’m a little confused how this works, is he reinstalling Linux/Ubuntu every week on all his machines? Or is it possible to “upgrade in place” just the kernel and leave your files/data alone, if the latter, is there a good guide for how to do that and for a homelabber would that be a good idea to avoid security bugs?
Yeah. I've never heard of reinstalling the OS just to get a newer kernel.
> is there a good guide for how to do that
I think it's best to continue to use your distro's package manager to handle actually installing that kernel, so the instructions would all be distro-specific. Some distros make working with a custom kernel easier than others.
> for a homelabber would that be a good idea to avoid security bugs?
Depends on your distro. I would expect major ones and enterprise-oriented ones to do a good job of backporting security fixes to the older kernels they run. If they do a really good job of this, it might even be more secure on the whole.
But yeah, just using the latest stable kernel is probably the simplest way to ensure that you have the latest security fixes. (It'll also ensure you have the latest undiscovered security bugs. ;)