At the time of this post, the download page linked in this blog post (and in Private VPN Service Recommendations and Comparison, No Sponsors or Ads - Privacy Guides) does not showcase these repos and still highlights the .deb and .rpm files. I reached out to Mullvad support about this and they said that a change to the download page for Linux is forthcoming:
Thanks for your feedback! We are happy to finally have our own
repository. There are indeed plans to update the Downloads page with
this as well. I think we will wait a while to collect feedback and to
decide the look of it.