It look to me that bwrap is trying to call nix, incase it is there.
Which is is not, as Nix at this time on Fedora must be installed via Copr.
I think rather the problem is with Bubblewrap / bwrap. I saw on a thread the other day someone having issues with glycin and bubblewrap and selinux permissions. Same issue? does not look like it is the same. But there are so many bugs in Gnome and KDE this release… Could be closely related. This is the thread.
Bubblewrap in installed by default on Gnome as Glycin uses it to sandbox images / image codecs.