This is the last I’ve seen here on this topic:
https://forums.opensuse.org/showthread.php/562547-XSCREENSAVER-no-longer-functional
I am on Leap 15.4, upgraded from 15.3 and many previous versions.
The update process loaded the xscreensaver 6.03 packages from the default repositories.
I have tried many of the included screensavers, and all of the GL ones. GLSlideshow is the only one that isn’t working for me.
This is the 15.4 / v 6.03 error message:
X error in glslideshow:
glslideshow: Failed request: 158
glslideshow: Major opcode: 151 ()
glslideshow: Resource id: 0x0
glslideshow: Serial number: 117 / 117
I have the full log but didn’t include it since it is nearly 800 lines long.
I submitted a full bug report to the author: https://www.jwz.org/xscreensaver/bugs.html
Manually installing xscreensaver v 5.44, from Open Suse 15.3 on 15.4 works with no problems.