I alt-clicked on a window's title bar and removed the bar by clicking "No border" but now I have no accessible means to restore that window's title bar. Is there a way to open KWin for that specific window? What are my options for restoring the window's border? (Plasma 5, if it's version-specific.)
Systemsettings > Application Style > Window Decorations
there should be an option to set borders.
or edit the following config file:
look for the line:
and either change it to false or comment it out.
ALT F3 -> more actions -> uncheck
I needed to do the same thing, but I didn't find anything relevant in ~/.config/kwinrc.
I found the application-specific settings in ~/.config/kwinrulesrc. I removed them with vim, and restarted kwin_x11, and restored the border on the program I had previously removed the border from.