I installed flutter as a snap on a Librem5 running PureOS (Debian Bullseye, Phosh/Phoc), compiled goguma and started it.
The phone shows an empty black window with grey titlebar "goguma" and on console I get the following error:
purism@pureos:~/Source/goguma/build/linux/arm64/release/bundle$ ./goguma
** (goguma:34059): WARNING **: 12:57:11.119: Failed to compile fragment shader: 0:2(1): error: No precision specified in this scope for type `vec2'
** (goguma:34059): WARNING **: 12:57:11.123: Failed to link program: error: linking with uncompiled/unspecialized shader
** (goguma:34059): CRITICAL **: 12:57:11.148: Failed to read XDG desktop portal settings: GDBus.Error:org.freedesktop.portal.Error.NotFound: Requested setting not found
** (goguma:34059): CRITICAL **: 12:57:11.156: Failed to read XDG desktop portal settings: GDBus.Error:org.freedesktop.portal.Error.NotFound: Requested setting not found
flutter: Warning: failed to initialize push controller: Exception: UnifiedPush not supported on this platform
flutter: dynamic_color: Accent color detected.
Sounds like a bug in either Flutter or Mesa. I'd suggest reporting to Flutter first.
Thanks for the answer! Just looked at the issues for flutter and found https://github.com/flutter/flutter/issues/152297 describing exactly the problem I wrote about here. It seems that flutter is broken and needs to be re-build from branch main of flutter.