While applications that do currently have Breeze versions (such as GIMP and Inkscape) do appear when installed from the distro's package manager, they will just show their normal icons when installed from sources like Flatpak. This could be fixed by symlinking the Flatpak icons to the normal icons.
Can you clarify what you mean by "symlinking the Flatpak icons to the normal icons"? What should the flatpak icons be named?
Here's a example from another icon pack, Papirus: https://github.com/PapirusDevelopmentTeam/papirus-icon-theme/blob/master/Papirus/64x64/apps/org.mozilla.firefox.svg
Oh I see, so we would need reverse DNS style names. Sure, I guess we can do that.
I started doing this by hand but got exhausted. Feels like the kind of thing that should be done programmatically at build time by having the necessary symlinks generated automatically according to a simple mapping in a text file or something. Maybe with a little Python script. :)
A possibly relevant merge request was started @ https://invent.kde.org/frameworks/breeze-icons/-/merge_requests/213
Git commit f6a1617865eb7d47f855618433988a972a8cfdc4 by Nate Graham, on behalf of Alois Wohlschlager. Committed on 28/03/2023 at 20:02. Pushed by ngraham into branch 'master'. Create symlinks for reverse DNS app identifiers When apps are installed using flatpak, the relevant icon is looked up under its reverse DNS app identifier, and not under its plain name. Create appropriate symlinks, so that flatpak-installed apps get their proper icons. FIXED-IN: 5.105 A +151 -0 create-app-symlinks.py M +3 -0 icons-dark/CMakeLists.txt M +10 -0 icons/CMakeLists.txt D +0 -1 icons/apps/48/com.github.ztefn.haguichi.svg D +0 -1 icons/apps/48/io.gitlab.Goodvibes.svg D +0 -1 icons/apps/48/org.inkscape.Inkscape.svg D +0 -1 icons/apps/48/org.kde.skanlite.svg D +0 -1 icons/apps/48/org.telegram.desktop.svg https://invent.kde.org/frameworks/breeze-icons/commit/f6a1617865eb7d47f855618433988a972a8cfdc4