Troubleshooting

Glimt writes what goes wrong to the terminal: start it from one (glimt ~/Pictures) to see it.

No window opens. The window needs OpenGL (EGL) and xkbcommon, which the .deb and .rpm install. With the .tar.gz or the AppImage on a minimal system, install libegl1 and libxkbcommon-x11-0 (Debian, Ubuntu) or libglvnd-egl and libxkbcommon-x11 (Fedora, RHEL). To try X11 instead of Wayland: env -u WAYLAND_DISPLAY glimt.
The AppImage does not start and speaks of FUSE: install fuse3 (or fuse), or run it with --appimage-extract-and-run.
HEIC, AVIF or videos show nothing. They are decoded by ffmpeg, which must be installed; HEIC needs ffmpeg and ffprobe 8.0 or newer.
Open, Copy or Move show no dialog. Install zenity (or kdialog on KDE).
Delete says gio is missing, or network shares do not open: install gio (glib, in libglib2.0-bin on Debian and Ubuntu) and GVfs.
A network share says the server is unknown. Many home servers are found only by their .local name or their address: try smb://nas.local/share or smb://192.168.1.10/share.
Import Lightroom Catalog says sqlite3 is missing. Install sqlite3 (Debian, Ubuntu) or sqlite (Fedora, RHEL).
A format of a decoder plugin shows nothing. The image area shows the decoder's error: check that its program is installed and run its Exec line by hand on the file. A decoder has 30 seconds and 512 MB, and new decoders are seen after a restart. See Plugins and formats.
Settings in a strange state. glimt --check-config tells what is wrong in the settings file, line by line, and Glimt tells the first of it when it starts. Or quit Glimt and remove ~/.config/glimt/config; the defaults come back.

Something else? Open an issue on GitHub.

Programs Glimt uses

Needed for	Program	Without it
Showing images	OpenGL 3 (Mesa, EGL), xkbcommon, Wayland or X11	no window
Open / Copy / Move dialogs	`zenity`	`kdialog`
Move to trash	`gio` (glib)	Delete says that gio is missing
Open With	`gio`	`xdg-open` (default application only)
smb://, sftp:// shares	`gio mount` (GVfs)	mount the share yourself
HEIC, AVIF, video	`ffmpeg`, `ffprobe`	not shown
Import Lightroom Catalog	`sqlite3`	the import says that sqlite3 is missing
Printing	`lp` (CUPS)	Save as PDF
A decoder plugin's format	the program its `Exec` line names	the image shows the program's error