When you run mkinitcpio it will include connected devices in the initrd.
Anything placed before the autodetect in the HOOKS array of mkinitcpio will be included even if it is not connected at the time when you generate the initrd. I assume this is what you meant with the autoload reference and it the way to get a multi-purpose initrd.
Keyboards rarely fails - if they do it is either completely dead or in case of brand new keyboards it is often single keys which - for some unknown reason produces a weird scan code not recognized for the expected key - and though it is rare for keyboard failure - multi-functional Windows programmable keyboards are those most prone to this behavior.
If you shutdown your - Dell G5 (laptop I suppose) - unplug the external keyboard before powering up - will it fail to recognize the built-in keyboard?
Have you tried with another keyboard you may have around?
As you mention Linux 4.19 - is this because the system is old or just a coincidence?
As you specifically mention you are able to use the keyboard when using a live boot - is this the new keyboard or the built-in keyboard?