I have done a bit of searching here for 'screensaver dual/multiple monitors', etc., but did not find much on point.

I am using a Dell XPS8920 with onboard Intel HD Graphics 630, and a AMD Radeon RX560 card installed. Each adapter is connected via HDMI output to a separate display at 1920x1080 resolution, and the multiple displays are in extended mode. I do most work and all settings on the main display (off the Radeon), but the Photos screensaver will only display on the secondary display (off the onboard Intel HD 630), while blanking the primary. 3D Text, Bubbles, Mystify, and Ribbons all leave the secondary display on, while showing only on the primary. Blank screensaver blanks both displays.

Is there any rhyme or reason here that I am missing? I would like to have the Photos output to both displays...