As summarized in title, GTK4 dialog doesn’t show thumbnails. But after visiting this directory once in Nautilus in icon view mode (thumbnail generated), then File picker works. Can some one else confirm the same?
Is it by design or a bug to be filed?
The bug report had already been filed upstream as: Automatically generate missing thumbnails in the new GTK4 FileChooser's grid icon view (#5663) · Issues · GNOME / gtk · GitLab
…but it was marked as a duplicate of the more technical (and less easily found) “Unix thumbnailing API” issue.
Same issue