If you want to build the SDL3 library for Linux right now today, you have to specify -DSDL_X11_XSCRNSAVER=OFF or it will assume that's what you wanted and take a hard dependency on the xscreensaver libraries

EDIT: To clarify based on things people have said in replies: It's not a linking dependency, but you DO need to either configure headers or disable the feature; the feature is for blocking the screensaver from activating during EG noninteractive cutscenes.