webp - no thumbnail in Thunar, regression of bugzilla 15706

Regression of https://bugzilla.xfce.org/show_bug.cgi?id=15706

Running Thunar 4.16.3 under Manjaro XFCE 20.2.1

Under usr/share/thumbnailers, my webp.thumbnailer

[Thumbnailer Entry]
Version=1.0
Encoding=UTF-8
Type=X-Thumbnailer
Name=webp Thumbnailer
MimeType=image/webp;
Exec=/usr/bin/convert -thumbnail %s %i %o

No thumbnail view