Offline, privacy focused open source android apps I use on a daily basis:

Basic phone apps from the 'Fossify' collection - https://search.f-droid.org/?q=fossify&lang=en (texts, calls, calculator, notes, clock)

**uLauncher. **Tiny, fast, minimal app launcher. - https://f-droid.org/packages/de.jrpie.android.launcher/

Aegis for 2FA - https://f-droid.org/en/packages/com.beemdevelopment.aegis/

**Immich **- for cloud storage of photos. https://f-droid.org/en/packages/app.alextran.immich/

has a google photos-like layout with indexing and searching. The indexing is done completely offline on your device. No data is sent anywhere.

ExifEraser - Wipe exif data from photos. Completely offline. https://github.com/Tommy-Geenexus/exif-eraser

**FUTO keyboard **- Fully offline keyboard with actually good autocorrect. https://keyboard.futo.org/

Joplin - Markdown notes, self-hosted through nextcloud to sync across devices. https://f-droid.org/en/packages/net.cozic.joplin/

LocalSend - Send files between your PC and phone through local network. https://f-droid.org/en/packages/org.localsend.localsend_app/

**Material files **- file manager with ability to initiate a local FTP server. https://f-droid.org/en/packages/me.zhanghai.android.files/

**Obtainium **- Download apps and app updates directly from associated github releases. https://f-droid.org/en/packages/dev.imranr.obtainium.fdroid/

**Outertune **- Alternate youtube music front-end with offline library support. https://f-droid.org/en/packages/com.dd3boh.outertune/

**SimplyTranslate **- Offline text translation (alternate privacy focused google translate front end) https://f-droid.org/en/packages/com.simplytranslate_mobile/

Termux - linux terminal emulator. https://f-droid.org/en/packages/com.termux/

Other apps I have been using for several years but are not open source but are completely offline with easily controllable permissions.

vivid ng - https://play.google.com/store/apps/details?id=com.ivianuu.oneplusgestures&hl=en-US

Custom navbar gestures with way better options than what is available by default. This app has been on my phone since I had a google nexus 4 and I cannot use my phone without it

swiftly switch - https://play.google.com/store/apps/details?id=org.de_studio.recentappswitcher.pro&hl=en-US
Another app I have been using since like 2016. Launch any number of apps on your phone from any screen with a single swipe. Again completely changed the way I use my phone and I cannot go back because of the muscle memory. No more going back home to open your app drawer. any app you want to open is always available no matter what screen you are currently in.