`scrcpy --otg` not working (on Linux)

- [ ✓] I have read the [FAQ](https://github.com/Genymobile/scrcpy/blob/master/FAQ.md).
- [ ✓] I have searched in existing [issues](https://github.com/Genymobile/scrcpy/issues).

**Environment**
- OS: Arch Linux
- scrcpy version: 2.2
- installation method: `pacman` (Arch's package manager; package: [https://archlinux.org/packages/extra/x86_64/scrcpy/](extra/scrcpy))
- device model: Google Pixel 6 Pro
- Android version: 14

**Issue**

`scrcpy` works:

```
$ scrcpy
scrcpy v2.2
INFO: ADB device found:
INFO: --> (usb) XXX device Pixel_6_Pro
/usr/share/scrcpy/scrcpy-server: 1 file pushed, 0 skipped. 54.9 MB/s (64363 bytes in 0.001s)
[server] INFO: Device: [Google] google Pixel 6 Pro (Android 14)
INFO: Renderer: opengl
INFO: OpenGL version: 4.6 (Compatibility Profile) Mesa 23.2.1-arch1.2
INFO: Trilinear filtering enabled
INFO: Texture: 1440x3120
```

However `scrcpy --otg` does not:

```
$ scrcpy --otg
scrcpy v2.2
ERROR: Could not find any USB device
```

Start by reproducing `scrcpy --otg` on Arch Linux with the reported Pixel 6 Pro, then compare its USB-device detection with ordinary `scrcpy`. Trace the `--otg` entry point and USB detection path; done means OTG finds the connected device and starts successfully.

Written by the indexing model from the issue text.