every week when I login into my Ubuntu with unattended updates enabled I see this: "system restart required".

the hot patch feature you mentioned is paid

Not to derail but there are issues with kernel patching. If it does work you start building a very large matrix of various levels of hot patches and then sometimes it just doesn’t.

On Ubuntu, when this message is shown, most of the updates except the kernel are already applied so you are mostly pretty secure. And you can choose when that will happen. And it’s just a normal reboot.

On Windows, IIRC, you are blocked during the whole update process which can take several minutes.