No need to duplicate the workflow, the workflow can have several on sections.

.github/workflows/nightly.yml

@@ -1,6 +1,7 @@
 name: Build and release nightly APK
 
 on:
+  workflow_dispatch:
   schedule:
     # Every nights at 4
     - cron: "0 4 * * *"

.github/workflows/nightly_manual.yml

@@ -1,43 +0,0 @@
-name: Build and release nightly APK manually
-
-on:
-  workflow_dispatch
-
-env:
-  GRADLE_OPTS: -Dorg.gradle.jvmargs="-Xmx3072m -Dfile.encoding=UTF-8 -XX:+HeapDumpOnOutOfMemoryError" -Dkotlin.daemon.jvm.options="-Xmx2560m" -Dkotlin.incremental=false
-  CI_GRADLE_ARG_PROPERTIES: --stacktrace -PpreDexEnable=false --max-workers 2 --no-daemon
-
-jobs:
-  nightly:
-    name: Build and publish nightly APK to Firebase
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v3
-      - name: Use JDK 17
-        uses: actions/setup-java@v3
-        with:
-          distribution: 'temurin' # See 'Supported distributions' for available options
-          java-version: '17'
-      - name: Install towncrier
-        run: |
-          python3 -m pip install towncrier
-      - name: Prepare changelog file
-        run: |
-          mv towncrier.toml towncrier.toml.bak
-          sed 's/CHANGES\.md/CHANGES_NIGHTLY\.md/' towncrier.toml.bak > towncrier.toml
-          rm towncrier.toml.bak
-          yes n | towncrier build --version nightly
-      - name: Build and upload Nightly APK
-        run: |
-          ./gradlew assembleNightly appDistributionUploadNightly $CI_GRADLE_ARG_PROPERTIES
-        env:
-          ELEMENT_ANDROID_NIGHTLY_KEYID: ${{ secrets.ELEMENT_ANDROID_NIGHTLY_KEYID }}
-          ELEMENT_ANDROID_NIGHTLY_KEYPASSWORD: ${{ secrets.ELEMENT_ANDROID_NIGHTLY_KEYPASSWORD }}
-          ELEMENT_ANDROID_NIGHTLY_STOREPASSWORD: ${{ secrets.ELEMENT_ANDROID_NIGHTLY_STOREPASSWORD }}
-          FIREBASE_TOKEN: ${{ secrets.ELEMENT_ANDROID_NIGHTLY_FIREBASE_TOKEN }}
-      - name: Additionally upload Nightly APK to browserstack for testing
-        continue-on-error: true # don't block anything by this upload failing (for now)
-        run: curl -u "$BROWSERSTACK_USERNAME:$BROWSERSTACK_PASSWORD" -X POST "https://api-cloud.browserstack.com/app-automate/upload" -F "file=@app/build/outputs/apk/nightly/app-universal-nightly.apk" -F "custom_id=element-x-android-nightly"
-        env:
-          BROWSERSTACK_USERNAME: ${{ secrets.ELEMENT_ANDROID_BROWSERSTACK_USERNAME }}
-          BROWSERSTACK_PASSWORD: ${{ secrets.ELEMENT_ANDROID_BROWSERSTACK_ACCESS_KEY }}