Thanks for pointing me in the right direction. I guess I will then use the scratchpad and create “fake taxonomy” that will be able to list all pages that used a particular shortcode call.
The second part I wonder then is whether the templates will be used in the correct order, i.e. if there’s a way to ensure whatever page I generate reading from such scratchpad is only created after every page has written there.
EDIT Alright, I suspect I found my answer in a related post I had overlooked before.
Hugo renders templates in parallel and caches results.
So on that note, I must be better off e.g. pre-processing the content files instead, i.e. have another tool swipe through it, look at the shortcodes and add tags to the front matter.