Good question!
The m-dot pages might not actually be indexed at all. Check out this article, and specifically the section I'm quoting:
https://searchengineland.com/google-advice-switch-m-dot-domain-responsive-mobile-first-index-rollout-277446
"The rationale is that right now, Google has a desktop-first index. So Google doesn’t really index your m-dot; they just annotate the m-dot URLs, but there is no true indexing of your m-dot content..."
You might first want to double-check that Google is actually indexing the mobile site as you suspect, or simply marking up search results with the subdomain. Mobile-first has been a slow rollout, which might not have hit you yet! This might help you check if you have indeed been moved:
https://blog.seoprofiler.com/google-check-log-files-find-site-moved-mobile-first-index/
If they are indexing, then yes - you'll have to make sure the URLs migrate appropriately to the new responsive site, and keep a close eye on mobile traffic changes in Search Console.
Hope this helps a bit!
Mike