I have installed a few programs via appimages. They have .desktop files in ~/.local/share/applications, however they don't show up in the launcher.

As in they aren't listed in any categories, or they don't show up when searching for them?
If you search for them in Krunner (Alt+F2) do they show up there?
I recall there being some update discrepancy where one would find the newly added shortcuts and the other wouldn't until later, or something. I don't remember the details, though (and it looks like it's probably been fixed).

You might edit the .desktop files and look for NoDisplay or OnlyShowIn directives, or anything else which would suggest why they wouldn't show up (in Plasma). Post an example if you need further assistance.

they aren't listed and don't show up in search, or in Krunner. The problem seems to lie in appimagelauncher. I'm seeing the following errors on the command line:

' at 15appimage_shall_not_be_integrated : Unexpected char '
AppImageLauncher error: appimage_shall_not_be_integrated() failed (returned -1)
' at 15appimage_is_terminal_app : Unexpected char '
AppImageLauncher error: appimage_is_terminal_app() failed (returned -1)
' at 15appimage_register_in_system : Malformed desktop entry: Unexpected char '