Thanks, Demm. This helped a lot.
First of all, it got me past my big mistake - I had assumed any KDE apps would come from Discover. Never occurred to me to try pacman!
Now spectacle is working, but I now have a different problem with kalarm. Here's the details on both:
For spectacle, tho you mention it is part of the Kaos install, it did not appear in the menu, nor did krunner find it. The "Prt Scr" key did nothing. I originally installed Kaos back in May and have kept it fully updated snce. I have no clue why it wasn't on my system.
BUT, I've now installed it with pacman, and it's in the menu, found by krunner, and opens with "Prt Scr", so all is good.
For kalarm, I also installed it using pacman, and it's now in the menu and found by krunner. However, when I try to run it, nothing happens, and I find this in journalctl:
Jan 12 18:00:27 F16 systemd[863]: Started KAlarm - Personal Alarm Scheduler.
Jan 12 18:00:27 F16 kalarm[3690]: /usr/bin/kalarm: error while loading shared libraries: libmpv.so.2: cannot open shared object file: No such file or directory
Jan 12 18:00:27 F16 systemd[863]: app-org.kde.kalarm@d3f37ad554014ec68683f77b7d36a999.service: Main process exited, code=exited, status=127/n/a
Jan 12 18:00:27 F16 systemd[863]: app-org.kde.kalarm@d3f37ad554014ec68683f77b7d36a999.service: Failed with result 'exit-code'.
pacman does not find any libmpv.so.2, so I'm not sure how to proceed from here.