Thanks for your report. It would be worthwhile to check if this is a bug that is already fixed in the newer version of xscreensaver 6.08 that is available in Debian unstable. Can you please try installing the 6.08 version from Debian unstable? If the binaries don't install as-is, the package can be safely rebuilt without changes on your Debian stable system. (Hopefully we can get 6.08 into bookworm-backports later.)
Regards, Tormod