A little trick if you have some thumbnails problem with SVG and PNG ( thumbnails have no background)
Clear thubmails cache:
rm -rf ~/.cache/thumbnails/*
Open your terminal and create/edit your profile's CSS file (if it doesn't already exist):
nano ~/.config/gtk-4.0/gtk.css
Copy and paste these lines inside:
.nautilus-window.view .thumbnail {
background: none;
box-shadow: none;
}
Save (Ctrl+O, Enter) and exit (Ctrl+X).
Restart Nautilus to see the change:
nautilus -q