diff --git a/.github/workflows/assemble.yml b/.github/workflows/assemble.yml
index 3e0e3157f..2b1de2b89 100644
--- a/.github/workflows/assemble.yml
+++ b/.github/workflows/assemble.yml
@@ -20,11 +20,11 @@ jobs:
         runs-on: ubuntu-latest
         steps:
             - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
-            - name: Set up JDK 17
+            - name: Set up JDK 21
               uses: actions/setup-java@03ad4de0992f5dab5e18fcb136590ce7c4a0ac95 # v5.6.0
               with:
                   distribution: "temurin"
-                  java-version: 17
+                  java-version: 21
             -   uses: gradle/actions/wrapper-validation@3f131e8634966bd73d06cc69884922b02e6faf92 # v6.2.0
             -   name: Setup JVM options
                 run: |
diff --git a/.github/workflows/check.yml b/.github/workflows/check.yml
index c7b2717ac..eb44c9ef0 100644
--- a/.github/workflows/check.yml
+++ b/.github/workflows/check.yml
@@ -21,11 +21,11 @@ jobs:
                 task: [ detekt, spotlessKotlinCheck, lint ]
         steps:
             - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
-            - name: Set up JDK 17
+            - name: Set up JDK 21
               uses: actions/setup-java@03ad4de0992f5dab5e18fcb136590ce7c4a0ac95 # v5.6.0
               with:
                   distribution: "temurin"
-                  java-version: 17
+                  java-version: 21
             -   name: Setup JVM options
                 run: |
                     mkdir -p "$HOME/.gradle"
diff --git a/.github/workflows/garm.yml b/.github/workflows/garm.yml
index b30a2bab6..2bab4042c 100644
--- a/.github/workflows/garm.yml
+++ b/.github/workflows/garm.yml
@@ -44,11 +44,11 @@ jobs:
                     docker exec --user www-data server /tmp/configNC.sh ${{ matrix.server }}
                     docker exec server /usr/local/bin/run.sh
 
-            -   name: set up JDK 17
+            -   name: set up JDK 21
                 uses: actions/setup-java@03ad4de0992f5dab5e18fcb136590ce7c4a0ac95 # v5.6.0
                 with:
                     distribution: "temurin"
-                    java-version: 17
+                    java-version: 21
 
             -   name: Enable KVM group perms
                 run: |
diff --git a/build.gradle b/build.gradle
index 2b44cdef6..c56ea9c81 100644
--- a/build.gradle
+++ b/build.gradle
@@ -37,11 +37,11 @@ subprojects {
     }
 }
 
-task clean(type: Delete) {
+tasks.register('clean', Delete) {
     delete rootProject.buildDir
 }
 
-task installGitHooks(type: Copy, group: "development") {
+tasks.register('installGitHooks', Copy) {
     def sourceFolder = "${rootProject.projectDir}/scripts/hooks"
     def destFolder = "${rootProject.projectDir}/.git/hooks"
 
diff --git a/gradle.properties b/gradle.properties
index f61f80964..38ac26b7a 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -16,19 +16,16 @@ android.nonTransitiveRClass=false
 android.nonFinalResIds=false
 
 # JVM arguments to optimize heap usage, enable heap dump on out-of-memory errors, and set the file encoding
-org.gradle.jvmargs=-Xmx4g -XX:MaxMetaspaceSize=1g -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8
+org.gradle.jvmargs=-Xmx3g -XX:MaxMetaspaceSize=1g -Dfile.encoding=UTF-8
 org.gradle.dependency.verification.console=verbose
-kotlin.daemon.jvmargs=-Xmx4096m
+kotlin.daemon.jvmargs=-Xmx3072m
 org.gradle.caching=true
 org.gradle.parallel=true
 org.gradle.configureondemand=true
 android.defaults.buildfeatures.resvalues=true
-android.sdk.defaultTargetSdkToCompileSdkIfUnset=false
-android.enableAppCompileTimeRClass=false
 android.usesSdkInManifest.disallowed=false
 android.uniquePackageNames=false
 android.dependency.useConstraints=true
-android.r8.strictFullModeForKeepRules=false
-android.r8.optimizedResourceShrinking=false
-android.builtInKotlin=false
-android.newDsl=false
+
+# Enabled parallel sync for Gradle 9.4+
+org.gradle.tooling.parallel=true
diff --git a/jitpack.yml b/jitpack.yml
index f0b5f2e60..d91129242 100644
--- a/jitpack.yml
+++ b/jitpack.yml
@@ -2,6 +2,6 @@
 # SPDX-FileCopyrightText: 2021-2023 Tobias Kaminsky <tobias@kaminsky.me>
 # SPDX-License-Identifier: MIT
 jdk:
-  - openjdk17
+  - openjdk21
 install:
   - ./gradlew :library:publishReleasePublicationToMavenLocal
diff --git a/library/build.gradle b/library/build.gradle
index 279159145..1ae7291e5 100644
--- a/library/build.gradle
+++ b/library/build.gradle
@@ -34,7 +34,6 @@ plugins {
 }
 
 apply plugin: 'com.android.library'
-apply plugin: 'kotlin-android'
 apply plugin: 'kotlin-parcelize'
 apply plugin: 'org.jetbrains.kotlin.plugin.serialization'
 apply from: "$rootProject.projectDir/jacoco.gradle"
@@ -159,12 +158,14 @@ android {
     }
 
     compileOptions {
-        sourceCompatibility JavaVersion.VERSION_17
-        targetCompatibility JavaVersion.VERSION_17
+        sourceCompatibility JavaVersion.VERSION_21
+        targetCompatibility JavaVersion.VERSION_21
     }
-	
-    kotlinOptions {
-        jvmTarget = '17'
+
+    kotlin {
+        jvmToolchain {
+            languageVersion.set(JavaLanguageVersion.of(21))
+        }
     }
 
     testOptions {
@@ -182,6 +183,12 @@ android {
     }
 
     namespace = 'com.owncloud.android.lib'
+
+    publishing {
+        singleVariant("release") {
+            withSourcesJar()
+        }
+    }
 }
 
 tasks.register("combinedTestReport", JacocoReport) {
diff --git a/sample_client/build.gradle b/sample_client/build.gradle
index a6b6b43dd..c6ecbda17 100644
--- a/sample_client/build.gradle
+++ b/sample_client/build.gradle
@@ -47,6 +47,12 @@ android {
 
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
     }
+
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_21
+        targetCompatibility JavaVersion.VERSION_21
+    }
+
     namespace = 'com.owncloud.android.lib.sampleclient'
     lint {
         abortOnError false
diff --git a/sample_client/src/main/java/com/owncloud/android/lib/sampleclient/MainActivity.java b/sample_client/src/main/java/com/owncloud/android/lib/sampleclient/MainActivity.java
index 035589b4c..0d32c04db 100644
--- a/sample_client/src/main/java/com/owncloud/android/lib/sampleclient/MainActivity.java
+++ b/sample_client/src/main/java/com/owncloud/android/lib/sampleclient/MainActivity.java
@@ -116,24 +116,19 @@ public void onDestroy() {
 
 
     public void onClickHandler(View button) {
-        switch (button.getId()) {
-            case R.id.button_refresh:
-                startRefresh();
-                break;
-            case R.id.button_upload:
-                startUpload();
-                break;
-            case R.id.button_delete_remote:
-                startRemoteDeletion();
-                break;
-            case R.id.button_download:
-                startDownload();
-                break;
-            case R.id.button_delete_local:
-                startLocalDeletion();
-                break;
-            default:
-                Toast.makeText(this, R.string.youre_doing_it_wrong, Toast.LENGTH_SHORT).show();
+        int id = button.getId();
+        if (id == R.id.button_refresh) {
+            startRefresh();
+        } else if (id == R.id.button_upload) {
+            startUpload();
+        } else if (id == R.id.button_delete_remote) {
+            startRemoteDeletion();
+        } else if (id == R.id.button_download) {
+            startDownload();
+        } else if (id == R.id.button_delete_local) {
+            startLocalDeletion();
+        } else {
+            Toast.makeText(this, R.string.youre_doing_it_wrong, Toast.LENGTH_SHORT).show();
         }
     }