https://bugs.kde.org/show_bug.cgi?id=507922
https://discuss.kde.org/t/sftp-root-directory/38039
Bug report says Dolphin but it's actually kio.
/ dir is impossible to get to via sftp or fish.
Downgrade to kio 6.15.0-1 if you want it to work like it's supposed to.
Edit: (Or not an edit it's a new post? Oh well)
It's this commit
https://github.com/KDE/kio/commit/883a16eb4ac808deceddf8ac3667ee888ff8ea60
I made a patch. At a guess the commit is treating / as a trailing slash instead of the root of the filesystem ? Whoops.
This is fixed in the next version.
that is a good hunch...