WSLg/Wayland: App hangs during startup unless --disable-gpu-compositing is supplied

## Summary

After forcing Fastmail to launch on Wayland, the application starts but no window appears.

The app only becomes usable when Electron is launched with:

--disable-gpu-compositing

## Environment

- Windows 11
- WSL2
- WSLg
- Flatpak
- Fastmail Flatpak: com.fastmail.Fastmail

## Reproduction

Launch:

```bash
flatpak run \
--env=XDG_SESSION_TYPE=wayland \
com.fastmail.Fastmail
```

Output:

```text
Running on native Wayland
Passing the following arguments to Electron:
--enable-wayland-ime
--wayland-text-input-version=3
```

Additional messages:

```text
[ERROR] drmGetDevices2() has not found any devices

Gdk-WARNING:
Failed to read portal settings:
GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod:
No such interface "org.freedesktop.portal.Settings"
```

The process remains running but no GUI window appears.

Waited approximately 2 minutes without success.

## Experiments

### Does NOT help

```bash
flatpak run \
--env=XDG_SESSION_TYPE=wayland \
com.fastmail.Fastmail \
--disable-gpu
```

Result:

- Process remains running
- No window appears

### Does NOT help

```bash
flatpak run \
--env=XDG_SESSION_TYPE=wayland \
com.fastmail.Fastmail \
--disable-gpu-sandbox
```

Result:

- Process remains running
- No window appears

### Works

```bash
flatpak run \
--env=XDG_SESSION_TYPE=wayland \
com.fastmail.Fastmail \
--disable-gpu-compositing
```

Result:

- Application starts
- Window appears
- Application is usable

### Also works

```bash
flatpak run \
--env=XDG_SESSION_TYPE=wayland \
com.fastmail.Fastmail \
--disable-gpu-compositing \
--disable-gpu
```

Result:

- Application starts
- Window appears
- Application is usable

## Expected Behavior

Fastmail should display its window without requiring:

```text
--disable-gpu-compositing
```

Start by reproducing the issue with the documented Flatpak command under WSL2/WSLg and native Wayland, then compare the Electron startup behavior with and without --disable-gpu-compositing. Investigate the reported drmGetDevices2 and portal-settings messages; done means the Fastmail window appears and is usable without requiring that flag.

Written by the indexing model from the issue text.