Again, disclaimer to not take my statements as gospel.

In this analogy, if I own a "8k HDR", dynamic metadata would be the same as the static one?

Yes.

For HDR this would be incredibly unlikely to happen though because it would require using whatever display the HDR content was mastered on (which is commonly a multi-thousand dollar mastering monitor, at least in the video production world).

Also, HGIG is something at software level, or do I need to find a tv compatible with HGIG?

The TV still needs to have it in order to communicate to the GPU what its capabilities are - thing of it like the EDID telling the GPU what resolution and refresh rate it is capable of.