Created attachment 136312 [details]
Screenshot of the dual-monitor setup

My laptop is connected to an external monitor, which I have set as the primary screen. The taskbar (panel) was appearing correctly onto that screen, until (I think) I tried out Wayland. Under Wayland, the panel appeared on the laptop. I might have disconnected the laptop from the monitor; I don't recall precisely. After learning that Wayland doesn't have the concept of a "primary screen" (to the chagrin of many users[1]), I edited the panel and dragged it onto the external monitor.

Due to numerous glitches in Wayland, I decided to go back to X11. I rebooted and logged in under X11. Now the panel appears on the laptop, even though the external monitor is set as primary. If I set the laptop as primary, the panel moves onto the external monitor.

[1]:
https://www.reddit.com/r/kde/comments/k7wa2d/how_do_i_set_the_primary_monitor_on_kde_wayland/
https://www.reddit.com/r/kde/comments/ae8czw/plasma_wayland_works_great_but_how_do_i_set_a/
https://www.reddit.com/r/kde/comments/ak3gfa/primary_monitor_with_wayland/