Found this on Reddit, hopefully it helps: https://www.reddit.com/r/kde/comments/1g0lpb9/comment/lrd4t1k/

Anything that runs as long as you want the block to be. Usually sleep is a good one, use sleep infinity if you want the blocker to never go away until the systemd-inhibit process is killed manually.

There is kde-inhibit --screenSaver <command> provided by KDE.

But these days, I would just recommend everyone to use systemd-inhibit --what=idle --why=<because> --who=<myself> <command> instead. Works across desktops and does the same thing.