You can update and it won't break anything, because Intel microcode won't be loaded into AMD CPUs. If you run apt show intel-microcode it tells you that there is a amd64-microcode package as well. If it is not already installed, you can install it, and then try to remove intel-microcode. If it doesn't want to remove anything else (e.g. the kernel), you can remove it. If not, just leave it installed.

you can remove firmware and other software that doesn't pertain to your system. the regular upgrade process will be shorter and you'll save some SSD space.

however, you'll lose the ability to take this SSD and plug it in a completely different system, like e.g. an intel laptop, and have it boot right up, unmodified.

If you don't have an Intel CPU, then you shouldn't need it. At least, I think it's only for CPUs and not for other intel-based devices (NIC, graphics, whatever).

It's prompting for upgrade because it's already installed. ~~It's recommended (but not required) by initramfs-tools, so that's probably why it's installed (recommended packages are installed by default).~~ oops, read that wrong. Intel-microcode recommends initramfs-tools.

You may want to run

apt-rdepends intel-microcode 

to see what pulled it in.

But you should be able to uninstall it, and then it won't prompt you any more.

The system packages don't adapt to your hardware. If you take your os drive out and stick it in another computer, you won't need to mess around making sure the CPU works properly. Unless you added more repositories, all your updates are coming from the same place, to trust any is to trust all.