feat: use the desktop's file picker on linux

README.md

@@ -27,6 +27,7 @@ works.
 | `0012-Launch-a-running-instance-...`       | A running instance can be started again on another account, with a console per copy.                                                       |
 | `0013-Explain-what-went-wrong-...`         | The Logs tab says what a crash was and offers a fix where there is one, without a connection.                                               |
 | `0014-Browse-skins-from-...`               | A Browse tab on the skin page: Ely.by's catalogue in the app, and NameMC, laby.net and crafty.gg in a window.                               |
+| `0015-Use-the-desktop-s-file-picker-...`   | File pickers on Linux are the desktop's own, such as KDE's, through the XDG desktop portal.                                                 |
 
 ### Offline accounts
 
@@ -96,6 +97,10 @@ A click with the middle mouse button on anything that scrolls starts autoscroll:
 to scroll until the next click, or hold and drag to scroll until you let go. Links and text fields
 keep their middle-click. Windows is left alone, since WebView2 autoscrolls by itself.
 
+File pickers on Linux go through the XDG desktop portal, so KDE shows its own dialog and GNOME its
+own, instead of a GTK dialog the AppImage themes as light Adwaita. Without a portal, GTK's dialog is
+used as before. Windows and macOS already use their native pickers.
+
 ### Skins
 
 With an Ely.by account selected, the skin page shows the account's skins on Ely.by: apply one, add

patches/0015-Use-the-desktop-s-file-picker-on-Linux.patch

@@ -0,0 +1,39 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Modrinth Enhanced <patches@modrinth-enhanced.invalid>
+Date: Tue, 15 Sep 2026 14:25:43 +0200
+Subject: [PATCH] Use the desktop's file picker on Linux
+
+File pickers - the webview's own, like the skin page's, and the dialog
+plugin's - are GtkFileChooserNative on Linux, which only uses the XDG
+desktop portal when asked. Unasked, it draws a GTK dialog, and inside the
+AppImage that dialog is themed as light Adwaita whatever the desktop
+looks like. GTK_USE_PORTAL is now set at startup, so KDE shows its own
+file dialog and GNOME its own. A player who set it already keeps their
+value, and without a portal GTK falls back to its own dialog as before.
+
+Windows and macOS already use the native pickers.
+---
+ apps/app/src/main.rs | 10 ++++++++++
+ 1 file changed, 10 insertions(+)
+
+diff --git a/apps/app/src/main.rs b/apps/app/src/main.rs
+index 04eedbd..4c269a3 100644
+--- a/apps/app/src/main.rs
++++ b/apps/app/src/main.rs
+@@ -115,6 +115,16 @@ async fn set_restart_after_pending_update(
+ // if Tauri app is called with arguments, then those arguments will be treated as commands
+ // ie: deep links or filepaths for .mrpacks
+ fn main() {
++    // File pickers on Linux - the webview's own and the dialog plugin's, both
++    // GtkFileChooserNative - go through the desktop portal, so KDE and GNOME
++    // show their own dialog rather than a GTK one the AppImage themes as
++    // Adwaita. Without a portal, GTK falls back to its own dialog.
++    #[cfg(target_os = "linux")]
++    if std::env::var_os("GTK_USE_PORTAL").is_none() {
++        // SAFETY: nothing else is running yet.
++        unsafe { std::env::set_var("GTK_USE_PORTAL", "1") };
++    }
++
+     #[cfg(feature = "export-app-events")]
+     theseus::export_app_event_bindings(
+         std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"))

scripts/check.sh

@@ -156,6 +156,8 @@ check "its corners are rounded" \
 	contains "$WORKTREE/apps/app-frontend/src/App.vue" "'rounded-window'"
 check "the middle button autoscrolls" \
 	contains "$WORKTREE/apps/app-frontend/src/App.vue" 'installAutoscroll()'
+check "file pickers use the desktop portal on Linux" \
+	contains "$WORKTREE/apps/app/src/main.rs" 'set_var("GTK_USE_PORTAL", "1")'
 
 log "No advertising or upsells"
 check "no Modrinth+ upsell in the app" \