Hi @fligi7!
Unfortunately my knowledge of the AWS provider specifically is not great enough to offer an answer to this follow-on question, but hopefully someone else in the forum will have some ideas. I do have some vague memory that the limitation here is in the underlying API (ec2:RunInstances) rather than in Terraform itself, where there’s only a single set of tags in that API which EC2 itself applies to all of the additional objects that are created as a side-effect, so I will admit I’m not optimistic that there is a different way to get this done.
My initial answer was focused on how to get the end result you wanted without declaring it all as a single resource, which I believe should be possible in the event that you can’t find a way to get the tagging result you want any other way.