Ah, I missed the zip file with the screenshots in. Yes, Akonadi loves RAM. I'm a bit confused as to why it's installed and running by default in this case - is this a Fedora-ism? I don't think Kubuntu or Arch install it by default, it's only installed as a dependency if you install elements of the KDEPIM suite.

FWIW, after baloo_file_extractor finished indexing new files on my Steam Deck, it exited, and KDE RAM usage was down to ~600MB.