gnome-text-editor version 45 will fix this issue. Before this release, , which for some reason was not able to use portals in snaps, but were able to use it in flatpaks. Gtk.FileChooserNative was usedGtk.FileDialog fixes it. I have two such snaps clapper, metadata-cleaner facing the same issue.
This is a related forum post.
EDIT: gnome-text-editor version 45 have not implemented Gtk.FileDialog yet. Sorry about that
https://gitlab.gnome.org/GNOME/gnome-text-editor/-/blob/main/src/editor-window-actions.c#L349