Application icon/logo not displaying in COSMIC, GNOME and KDE (Flatpak prep)

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Hello Fedora Community,

I am currently developing “Lilith Browser”, a secure hybrid browser built with Python (pywebview/Tkinter), Rust (Maturin), and an isolated network layer.

I am looking for guidance to make my application logo fully compliant with modern Linux desktop standards. Currently, I cannot get the icon to display correctly in the new COSMIC desktop environment (Cosmic Files/Panel), and I want to ensure native compatibility across GNOME, KDE Plasma, and Fedora Atomic workstations.

Here is my current logo asset:

I need help with two main issues:

  1. Format Optimization: I want to optimize this asset into a scalable vector format (SVG) and proper fixed raster sizes (PNG) in 64x64, 128x128, 256x256, and 512x512 pixels.
  2. Freedesktop Integration: I need to ensure the desktop entry file (org.lilith.browser.desktop) successfully maps the launcher icon in all app grids (GNOME Shell, Cosmic App List, KDE Kickoff) and complies with Freedesktop AppStream metadata requirements for Flatpak/Flathub distribution.

If any icon designer or Fedora packaging expert could point out why COSMIC might be dropping the icon cache or help me clean up the assets for modern desktops, I would deeply appreciate it!

Thank you for your help,
Laura

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I recommend looking at the recommendations from Flathub around desktop files, app icons, metadata info, etc. as those apply beyond Flatpak and should help you here.