Created attachment 8108
Installed xfce4-screensaver to 19.04 via experimental ppa.
Works as expected.
Installed xscreensaver-data to get more screensaver options. None of the new listed screensavers work.
Got a possible help from .xsession-errors:
(xfce4-screensaver-preferences:16703): xfconf-CRITICAL **: 11:32:22.897: IA__xfconf_channel_set_string_list: assertion 'XFCONF_IS_CHANNEL(channel) && property && values && values' failed
I can confirm that the screensavers do not seem to work with xfce4-screensaver in 19.04. They do work with mate-screensaver, so there may be some additional flags needed at build time. I'll continue looking into this.
Sean Davis referenced this bugreport in commit cd6e2e20db505fd1934d3b5a54bf07470e81c441
Add /usr/lib and /usr/libexec as trusted engine paths (bug #14883) - Enables local installs with access to existing screensavers
Confirmed that the above patch resolves the issue in 19.04.
Why Re-add these hard code path? On some systems xscreensaver files are not located in /usr/lib and /usr/libexec and additional screensavers are not displayed in settings dialog.
In configure script there are 2 options for that (it is packager to define these 2 variables) :
Otherwise, packager also need to run data/migrate-xscreensaver-config.sh script in order to convert Xscreensaver's engine to xfce4-screensaver.