So if this happened to you, you might want to consider this.

The problem (for me but it could happen to you) is that I used libraries like ffmpeg_kit_flutter_new and just_audio. Somehow, R8 which is google's code shrinker/obfuscator strips down bridging classes that causes the immidiate crash. App worked on debug because R8 doesn't run in debug.

buildTypes {
    release {
        signingConfig = signingConfigs.getByName("debug")
        isMinifyEnabled = false
    }
}

if there's still errors use,

buildTypes {
    release {
        signingConfig = signingConfigs.getByName("debug")
        isMinifyEnabled = false
        isShrinkResources = false
    }
}

isMinifyEnabled = false -- is the minimal solution

I thought at first it was caused by Impeller but it wasn't. Note, I don't know if this is a permanent fix, though Claude said that a good pro-guard is permanent.