OpenTTD can't play music (Can't reach any soundfont)

Hello!

This is an issue that [I reported to the official Minigalaxy bug tracker](https://github.com/sharkwouter/minigalaxy/issues/707), but before some time and testing, It was a two part issue, one with Fluidsynth not working properly before, but I fixed, and other part that It is only happening with the Flatpak version.

Basically, [OpenTTD](https://www.gog.com/en/game/openttd) can't can't play music with Minigalaxy Flatpak version. It uses MIDI, so I need Fluidsynth daemon working to make it work. But the game can't reach Fluidsynth:

```
$ flatpak run --branch=stable --arch=x86_64 --command=minigalaxy io.github.sharkwouter.Minigalaxy
Running OpenTTD
[2026-06-17 22:41:40] dbg: [driver:1] Successfully loaded blitter '32bpp-anim'
[2026-06-17 22:41:40] dbg: [driver:2] Resolution for display: 1600x900
[2026-06-17 22:41:40] dbg: [driver:1] SDL2: Mouse is at (943, 729), use display 0 (0, 0, 1920, 1080)
[2026-06-17 22:41:40] dbg: [driver:1] SDL2: using mode 1600x900
[2026-06-17 22:41:41] dbg: [driver:1] SDL2: using driver 'x11'
[2026-06-17 22:41:41] dbg: [driver:1] OpenGL driver: AMD - AMD Radeon Vega 10 Graphics (radeonsi, raven, ACO, DRM 3.64, 7.0.0-22-generic) (4.6 (Compatibility Profile) Mesa 26.0.6 (git-0e095aab43))
[2026-06-17 22:41:41] dbg: [driver:3] OpenGL: Using persistent buffer mapping
[2026-06-17 22:41:41] dbg: [driver:2] OpenGL shading language version: 4.60, texture units = 160
[2026-06-17 22:41:41] dbg: [driver:1] Successfully probed video driver 'sdl-opengl'
[2026-06-17 22:41:41] dbg: [driver:1] Successfully probed sound driver 'sdl'
[2026-06-17 22:41:41] dbg: [driver:1] Fluidsynth: sf (null)
[2026-06-17 22:41:41] dbg: [driver:1] Fluidsynth: Failed to load config file '/etc/fluidsynth.conf' - file doesn't exist
[2026-06-17 22:41:41] dbg: [driver:1] Fluidsynth: Failed to load config file '/home//.fluidsynth' - file doesn't exist
[2026-06-17 22:41:41] dbg: [driver:1] Fluidsynth: samplerate 44100
[2026-06-17 22:41:41] dbg: [driver:1] Probing music driver 'fluidsynth' failed with error: Could not open any sound font
[2026-06-17 22:41:41] dbg: [driver:1] Successfully probed music driver 'extmidi'
[2026-06-17 22:41:41] dbg: [driver:1] using thread for game-loop
[2026-06-17 22:41:41] dbg: [driver:1] Switching blitter from '32bpp-anim' to '40bpp-anim'...
[2026-06-17 22:41:41] dbg: [driver:1] Successfully loaded blitter '40bpp-anim'
[2026-06-17 22:41:41] dbg: [driver:1] Successfully switched to 40bpp-anim.
[2026-06-17 22:41:41] dbg: [driver:1] SDL2: using mode 1600x900
[2026-06-17 22:41:41] dbg: [driver:1] extmidi: set volume not implemented
```

With normal Minigalaxy (The non-flatpak version), the music works.

```
$ minigalaxy
Running OpenTTD
[2026-06-17 22:43:27] dbg: [driver:1] Successfully loaded blitter '32bpp-anim'
[2026-06-17 22:43:27] dbg: [driver:2] Resolution for display: 1600x900
[2026-06-17 22:43:27] dbg: [driver:1] SDL2: Mouse is at (975, 736), use display 0 (0, 0, 1920, 1080)
[2026-06-17 22:43:27] dbg: [driver:1] SDL2: using mode 1600x900
[2026-06-17 22:43:27] dbg: [driver:1] SDL2: using driver 'x11'
[2026-06-17 22:43:27] dbg: [driver:1] OpenGL driver: AMD - AMD Radeon Vega 10 Graphics (radeonsi, raven, ACO, DRM 3.64, 7.0.0-22-generic) (4.6 (Compatibility Profile) Mesa 26.0.3-1ubuntu1)
[2026-06-17 22:43:27] dbg: [driver:3] OpenGL: Using persistent buffer mapping
[2026-06-17 22:43:27] dbg: [driver:2] OpenGL shading language version: 4.60, texture units = 160
[2026-06-17 22:43:27] dbg: [driver:1] Successfully probed video driver 'sdl-opengl'
[2026-06-17 22:43:27] dbg: [driver:1] Successfully probed sound driver 'sdl'
[2026-06-17 22:43:27] dbg: [driver:1] Fluidsynth: sf (null)
[2026-06-17 22:43:27] dbg: [driver:1] Fluidsynth: Failed to load config file '/etc/fluidsynth.conf' - file doesn't exist
[2026-06-17 22:43:27] dbg: [driver:1] Fluidsynth: Failed to load config file '/home//.fluidsynth' - file doesn't exist
[2026-06-17 22:43:27] dbg: [driver:1] Fluidsynth: samplerate 44100
[2026-06-17 22:43:27] dbg: [driver:1] Successfully probed music driver 'fluidsynth'
[2026-06-17 22:43:28] dbg: [driver:1] using thread for game-loop
[2026-06-17 22:43:28] dbg: [driver:1] Switching blitter from '32bpp-anim' to '40bpp-anim'...
[2026-06-17 22:43:28] dbg: [driver:1] Successfully loaded blitter '40bpp-anim'
[2026-06-17 22:43:28] dbg: [driver:1] Successfully switched to 40bpp-anim.
[2026-06-17 22:43:28] dbg: [driver:1] SDL2: using mode 1600x900
fluidsynth: Ignoring unrecognized meta event type 0x21
fluidsynth: Ignoring unrecognized meta event type 0x21
fluidsynth: Ignoring unrecognized meta event type 0x21
fluidsynth: Ignoring unrecognized meta event type 0x21
fluidsynth: Ignoring unrecognized meta event type 0x21
fluidsynth: Ignoring unrecognized meta event type 0x21
fluidsynth: Ignoring unrecognized meta event type 0x21
fluidsynth: Ignoring unrecognized meta event type 0x21
fluidsynth: Ignoring unrecognized meta event type 0x21
```

Both Minigalaxy game installs are in fact the same, as they point to the same folder.

At first, with some research, one culprit can be that It seems that OpenTTD [has hardcoded the paths of the soundfonts](https://github.com/OpenTTD/OpenTTD/blob/ae917cb8c61aea7fe1bd0738f52354f59654aa48/src/music/fluidsynth.cpp#L32-L52) as I realised It wasn't using the one that I have configured, and It can't find the fluidsynth config file (It looks for `/etc/fluidsynth` or `~/fluidsynth`, but they are in `/etc/default/fluidsynth` and `~/.config/fluidsynth` in my system, but that's their issue, although any of the fallbacks maybe should work and they don't in the flatpak environment).

Thanks in advance!

-----

**Update**: It's seems, in fact, the issue is OpenTTD can't find any soundfont, even the ones hardcoded. The only way to have music is create a `~/.fluidsynth` but using the new config file format introduced in 2.5.0 (System fluidsynth is 2.4.8, so those config files don't work):

```
set synth.default-soundfont /home/user/.local/share/soundfonts/default.sf2
```

And then allow to Minigalaxy flatpak (with Flatseal, for example) to access `~/.fluidsynth` and wherever is the Soundfont (can't be `/usr/`, is not allowed). With _that_, there is music in OpenTTD GOG version with the Minigalaxy Flatpak.

So, unless It's added a valid Soundfont in Minigalaxy that can use OpenTTD (one from the hardcoded paths, for example), there is not gonna have music, unless you customized one in this way.