Remmina - The GTK+ Remote Desktop Client  v1.4.33
Remmina is a remote desktop client written in GTK+, aiming to be useful for system administrators and travellers, who need to work with lots of remote computers in front of either large monitors or tiny netbooks. Remmina supports multiple network protocols in an integrated and consistent user interface. Currently RDP, VNC, NX, XDMCP and SSH are supported.
Unrecognized image format

If you get errors like:

Gtk:ERROR:../src/gtk/gtkiconhelper.c:494:ensure_surface_for_gicon: assertion failed (error == NULL): Failed to load /snap/remmina/x1/share/icons/Adwaita/16x16/status/image-missing.png: Unrecognized image file format (gdk-pixbuf-error-quark, 3)
Bail out! Gtk:ERROR:../src/gtk/gtkiconhelper.c:494:ensure_surface_for_gicon: assertion failed (error == NULL): Failed to load /snap/remmina/x1/share/icons/Adwaita/16x16/status/image-missing.png: Unrecognized image file format (gdk-pixbuf-error-quark, 3)
[1] 1942628 abort (core dumped) G_MESSAGES_PREFIXED=all G_MESSAGES_DEBUG=all snap run remmina

Run this command

sudo update-mime-database /usr/share/mime

Saving crash Remmina

Sometimes is an AppArmor issue that can be solved with:

sudo dpkg-reconfigure apparmor

Sometimes you need to remove and install again Remmina (the hard way)

# Backup your .remmina and remmina.pref files under /home/<username>/snap/remmina, after
sudo snap remove remmina
# reboot (sadly)
sudo snap install remmina
# restore your profiles and Remmina preferences

Cannot connect to Windows server

Often is because the installed ffmpeg doesn't contain required codecs.

Running Remmina in debug mode will show these errors:

[17:04:30:233] [9:90] [ERROR][com.freerdp.codec] - Failed to initialize libav parser
[17:04:30:233] [9:90] [ERROR][com.freerdp.core.codecs] - Failed to create h264 codec context

That you can solve with:

flatp install org.freedesktop.Platform.ffmpeg-full -y