Flatpak scaling issue on Fedora COSMIC

[givensuman]

Wondering if anyone has dealt with this issue or has suggestions on what to do about it. Some Flatpak applications have scaling issues and appear zoomed in.

[tadpole256]

This looks like a portal / Wayland scaling mismatch, not an issue with the Flatpak itself.

Flatpak apps usually rely on xdg-desktop-portal (and the desktop-specific backend) to learn things like scale factor. If the COSMIC portal backend is missing, not selected, or misreporting scale, some apps can come up “zoomed in” like your screenshots. 

Things to check:

1. Confirm what portal backend is actually being used
   • echo $XDG_CURRENT_DESKTOP
   • systemctl --user status xdg-desktop-portal
   • systemctl --user status xdg-desktop-portal-cosmic

2. If COSMIC portal is not installed or not being picked
   • Make sure xdg-desktop-portal-cosmic is installed (and up to date for your distro packaging).
   • If Fedora’s COSMIC packaging does not include it yet, installing xdg-desktop-portal-gtk can sometimes “fix” Flatpak behavior by giving it a usable backend, though it is not ideal long-term. (People have reported portal backend swaps changing Flatpak behavior in COSMIC.) 

3. Workaround: force a sane scale inside the Flatpak
   • For GTK apps:
   • flatpak override --user --env=GDK_SCALE=1 --env=GDK_DPI_SCALE=1
   • For Qt apps:
   • flatpak override --user --env=QT_SCALE_FACTOR=1
   • Then restart the app.

If you paste your current display scale setting (100/125/150/200), plus output of the 3 commands above, we can narrow down whether this is fractional scaling or the portal backend selection.

[givensuman]

$  journalctl --user -u xdg-desktop-portal -b | tail -200
Journal file /var/log/journal/e111d7a5903341ffa439ace17ce684ae/user-1000@0006472299c48f2b-46c369f0fde10631.journal~ is truncated, ignoring file.
Feb 01 13:33:21 gandalf systemd[2136]: Starting xdg-desktop-portal.service - Portal service...
Feb 01 13:33:21 gandalf /usr/libexec/xdg-desktop-portal[2660]: Choosing gtk.portal for org.freedesktop.impl.portal.AppChooser as a last-resort fallback
Feb 01 13:33:21 gandalf /usr/libexec/xdg-desktop-portal[2660]: Choosing gtk.portal for org.freedesktop.impl.portal.Print as a last-resort fallback
Feb 01 13:33:21 gandalf /usr/libexec/xdg-desktop-portal[2660]: Choosing gtk.portal for org.freedesktop.impl.portal.Notification as a last-resort fallback
Feb 01 13:33:21 gandalf /usr/libexec/xdg-desktop-portal[2660]: Choosing gtk.portal for org.freedesktop.impl.portal.Inhibit as a last-resort fallback
Feb 01 13:33:21 gandalf /usr/libexec/xdg-desktop-portal[2660]: Choosing gtk.portal for org.freedesktop.impl.portal.Account as a last-resort fallback
Feb 01 13:33:21 gandalf /usr/libexec/xdg-desktop-portal[2660]: Choosing gtk.portal for org.freedesktop.impl.portal.Email as a last-resort fallback
Feb 01 13:33:21 gandalf /usr/libexec/xdg-desktop-portal[2660]: Choosing gtk.portal for org.freedesktop.impl.portal.DynamicLauncher as a last-resort fallback
Feb 01 13:33:21 gandalf systemd[2136]: Started xdg-desktop-portal.service - Portal service.

"gtk.portal as a last-restort fallback" seems to suggest your intuition is correct, unless we would expect a specific mention of org.freedesktop.portal.Flatpak

$  busctl --user list | grep -I portal.desktop.cosmic
org.freedesktop.impl.portal.desktop.cosmic                                                   2781 xdg-desktop-por given :1.104        user@1000.service -       -

[tadpole256]

Those “gtk.portal as a last-resort fallback” messages are expected for the interfaces COSMIC does not implement. Your cosmic.portal only provides Access/FileChooser/Screenshot/Settings/ScreenCast, so xdg-desktop-portal will fall back to GTK for Notification/Print/AppChooser/Inhibit/etc.

The important part is whether the Settings portal is coming from COSMIC (since scaling hints often come from Settings) and what values it reports. Can you run:
journalctl --user -u xdg-desktop-portal -b | grep -i settings
and also:
gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.Settings.Read org.gnome.desktop.interface scaling-factor
gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.Settings.Read org.gnome.desktop.interface text-scaling-factor

If the zoomed apps are Electron Flatpaks, a workaround is flatpak override --user --env=ELECTRON_OZONE_PLATFORM_HINT=wayland which often fixes fractional scaling issues.

[givensuman]

No dice :(

$  journalctl --user -u xdg-desktop-portal -b | grep -i settings
Journal file /var/log/journal/e111d7a5903341ffa439ace17ce684ae/user-1000@0006472299c48f2b-46c369f0fde10631.journal~ is truncated, ignoring file.

$  gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.Settings.Read org.gnome.desktop.interface scaling-factor
Error: GDBus.Error:org.freedesktop.portal.Error.NotFound: Requested setting not found

$  gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.Settings.Read org.gnome.desktop.interface text-scaling-factor
Error: GDBus.Error:org.freedesktop.portal.Error.NotFound: Requested setting not found

Before making this post I've tried various combinations of the following environment variables in /usr/share/flatpak/overrides/global to no avail

GDK_SCALE=1
GDK_DPI_SCALE=1
QT_AUTO_SCREEN_SCALE_FACTOR=0
QT_SCALE_FACTOR=1
QT_FONT_DPI=96
GDK_BACKEND=wayland
QT_QPA_PLATFORM=wayland
ELECTRON_OZONE_PLATFORM_HINT=wayland
XWAYLAND_NO_GLAMOR=1
MOZ_ENABLE_WAYLAND=1
SDL_VIDEODRIVER=wayland
CLUTTER_BACKEND=wayland

[tadpole256]

The Settings.Read org.gnome.desktop.interface scaling-factor failures are to be expected. The Settings portal only standardizes a very small set of keys (docs currently only list org.freedesktop.appearance color-scheme), and GNOME’s scaling keys are not guaranteed to exist via the portal. 

Next steps:

1. Find out what the portal does expose:
   gdbus call --session --dest org.freedesktop.portal.Desktop --object-path /org/freedesktop/portal/desktop --method org.freedesktop.portal.Settings.ReadAll ""

2. I suspect your Flatpak overrides are not being read. /usr/share/flatpak/overrides/global is likely not used. Overrides are typically under $XDG_DATA_HOME/flatpak/overrides (usually ~/.local/share/flatpak/overrides/) for user overrides, or /var/lib/flatpak/overrides/ for system. 

Can you paste flatpak override --user --show and flatpak override --system --show plus one example app-id that is zooming? If it is an Electron app, once overrides are applied from the correct location, flatpak override --user --env=ELECTRON_OZONE_PLATFORM_HINT=wayland is a good test.

[givensuman]

I suspect your Flatpak overrides are not being read.

I got some bad intel on that one. Setting

[Environment]
GDK_SCALE=1
QT_SCALE_FACTOR=1
GDK_BACKEND=wayland
QT_QPA_PLATFORM=wayland
ELECTRON_OZONE_PLATFORM_HINT=auto

in ~/.local/share/flatpak/overrides/global resolves the issue on all apps I have tried. Thank you so much for your patient help <3