After upgrading (I think. The timing is about right, but I'm not fully sure) to plasma-desktop-5.17.4-2.fc31.x86_64, my compose key no longer...composes. I have tried changing which key is assigned, but it does not matter. When set to Right Ctrl, typing <Right Ctrl>+-+-+- in a terminal or web browser decreases the zoom level instead of typing an em dash. When set to other keys (e.g. Pause or Right Ctrl), nothing is typed. This has persisted with plasma-desktop-5.17.5-1 and occurs on multiple machines.
I believe this is a dup of bug #1787190 (krunner got new associations that may have stomped on this) *** This bug has been marked as a duplicate of bug 1787190 ***