But checking again, it's probably that they are using an older build tools to sign, I would try with 30.
These are the steps that worked for me:
1. Download your command tools from android
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and unzip
2. Use the sdkmanager binary inside /cmdline-tools/bin to download some build tools, running: ./sdkmanager --sdk_root=. "build-tools;30.0.0"
3. With java installed, create a certificate: keytool -genkey -alias alias -keyalg RSA -keypass changeit -storepass changeit -keystore keystore.jks
4. With the build tools you downloaded, use zipalign (inside build-tools/30.0.0):
./zipalign 4 Sweet_Affection_0.8.1.apk Sweet_Affection_0.8.1_NEW.apk
5. Now sign with apksigner (inside build-tools/30.0.0):
./apksigner sign --ks keystore.jks Sweet_Affection_0.8.1_NEW.apk
5. Install the APK. You have adb in platform-tools if you want to run: ./adb install Sweet_Affection_0.8.1_NEW.apk
As they are not trivial at all, I've uploaded the APK to
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Install at your own risk, it could not work in your phone. Renpy takes a while (20 seconds) to load even in a beefy device.