This gist contains almost all the pro guard rules that you will ever need for R8

proguard_rules.pro

# Add project specific ProGuard rules here.
# You can control the set of applied configuration files using the
# proguardFiles setting in build.gradle.
#
# For more details, see
#   http://developer.android.com/guide/developing/tools/proguard.html

# If your project uses WebView with JS, uncomment the following
# and specify the fully qualified class name to the JavaScript interface
# class:
#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
#   public *;
#}

# Uncomment this to preserve the line number information for
# debugging stack traces.
#-keepattributes SourceFile,LineNumberTable

# If you keep the line number information, uncomment this to
# hide the original source file name.
#-renamesourcefileattribute SourceFile


#-------------------------------------------------
# JetPack Navigation
# This fixes: Caused by: androidx.fragment.app.Fragment$InstantiationException: Unable to instantiate fragment androidx.navigation.fragment.NavHostFragment: make sure class name exists
#-------------------------------------------------
-keepnames class androidx.navigation.fragment.NavHostFragment
-keepnames class com.yourapp.app.models.** {public private protected *; }
-keepnames class * extends android.os.Parcelable

# These options are the minimal options for a functioning application
-keep class org.apache.commons.logging.**               { *; }
-keepattributes Signature,*Annotation*,EnclosingMethod

-keep public class com.google.firebase.** {*;}
-keep class com.google.android.gms.internal.** {*;}
-keepclasseswithmembers class com.google.firebase.FirebaseException

-dontwarn org.apache.commons.logging.impl.**
-dontwarn org.apache.http.conn.scheme.**
-dontwarn org.apache.http.annotation.**

## -------------Begin: Retrofit2 ---
-dontwarn retrofit2.**
-keep class retrofit2.** { *; }
-keepattributes Signature
-keepattributes Exceptions
-keepattributes *Annotation*

-keepclasseswithmembers class * {
    @retrofit2.http.* <methods>;
}
-keepclassmembernames interface * {
        @retrofit.http.* <methods>;
}

## -------------End: Retrofit2 ---
##---- keep your interface names {*;}

-keep interface com.yourapp.yourinterfacepackage

# removes such information by default, so configure it to keep all of it.
-keepattributes Signature

# For using GSON @Expose annotation
-keepattributes *Annotation*

-ignorewarnings
-flattenpackagehierarchy
-keepattributes SourceFile,LineNumberTable
-renamesourcefileattribute SourceFileOfException


#### OkHttp, Retrofit and Moshi
-dontwarn okhttp3.**
-dontwarn retrofit2.Platform.Java8
-dontwarn okio.**
-dontwarn javax.annotation.**
-keepclasseswithmembers class * {
    @retrofit2.http.* <methods>;
}

-keepclasseswithmembers class * {
    @com.squareup.moshi.* <methods>;
}

-keep @com.squareup.moshi.JsonQualifier interface *

# Enum field names are used by the integrated EnumJsonAdapter.
# values() is synthesized by the Kotlin compiler and is used by EnumJsonAdapter indirectly
# Annotate enums with @JsonClass(generateAdapter = false) to use them with Moshi.
-keepclassmembers @com.squareup.moshi.JsonClass class * extends java.lang.Enum {
    <fields>;
    **[] values();
}

# Keep helper method to avoid R8 optimisation that would keep all Kotlin Metadata when unwanted
-keepclassmembers class com.squareup.moshi.internal.Util {
    private static java.lang.String getKotlinMetadataClassName();
}

-keep class kotlin.Metadata { *; }
-keepclassmembers class kotlin.Metadata {
    public <methods>;
}

-keepclassmembers class * {
    @com.squareup.moshi.FromJson <methods>;
    @com.squareup.moshi.ToJson <methods>;
}

-keepnames @kotlin.Metadata class com.yourpackage.model.**
-keep class com.yourpackage.model.** { *; }
-keepclassmembers class com.yourpackage.model.** { *; }

# Retrofit does reflection on generic parameters. InnerClasses is required to use Signature and
# EnclosingMethod is required to use InnerClasses.
-keepattributes Signature, InnerClasses, EnclosingMethod

# Retrofit does reflection on method and parameter annotations.
-keepattributes RuntimeVisibleAnnotations, RuntimeVisibleParameterAnnotations

# Keep annotation default values (e.g., retrofit2.http.Field.encoded).
-keepattributes AnnotationDefault

# Retain service method parameters when optimizing.
-keepclassmembers,allowshrinking,allowobfuscation interface * {
    @retrofit2.http.* <methods>;
}

# Ignore annotation used for build tooling.
-dontwarn org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement

# Ignore JSR 305 annotations for embedding nullability information.
-dontwarn javax.annotation.**

# Guarded by a NoClassDefFoundError try/catch and only used when on the classpath.
-dontwarn kotlin.Unit

# Top-level functions that can only be used by Kotlin.
-dontwarn retrofit2.KotlinExtensions
-dontwarn retrofit2.KotlinExtensions.*

# With R8 full mode, it sees no subtypes of Retrofit interfaces since they are created with a Proxy
# and replaces all potential values with null. Explicitly keeping the interfaces prevents this.
-if interface * { @retrofit2.http.* <methods>; }
-keep,allowobfuscation interface <1>

# Keep generic signature of Call, Response (R8 full mode strips signatures from non-kept items).
-keep,allowobfuscation,allowshrinking interface retrofit2.Call
-keep,allowobfuscation,allowshrinking class retrofit2.Response

# With R8 full mode generic signatures are stripped for classes that are not
# kept. Suspend functions are wrapped in continuations where the type argument
# is used.
-keep,allowobfuscation,allowshrinking class kotlin.coroutines.Continuation

Thanks for sharing!