I don't know exactly what comes on the OnePlus to say what you should delete, so it's probably a good idea to search that up.

As an alternative to the Play Store you have F-Droid (not really an alternative, more like a complementary open source store). I personally recommend the Neo Store client. which is pretty, easy to use and have a lot of repositories for apps built-in, you just need to activate the ones you want in the settings, with F-Droid and IzzyOnDroid repos active you're basically covered. I also recommend you use Obtainium as it let's you download apps directly from GitHub and other sources, including F-Droid itself. I consider it a must because one downside of F-Droid is that sometimes apps are not updated for a long time there, so you have a way to update an app if you need too, and it is also useful for apps that are not on F-Droid.

Now for other apps, I do have some alternatives I can recommend:

• Authenticator (2FA) > Aegis Authenticator
• Calculator > OpenCalc
• Clock/Alarm > Chrono
• Document Scanner > OSS Document Scanner
• Files > Material Files
• Gallery > Aves (IzzyOnDroid, Play Store)
• Keyboard > Heliboard (it's ok, but could be better) or Florisboard/Florisboard Beta (usable but incomplete, it's very promising)
• Launcher > Lawnchair (like Pixel Launcher and Nova Launcher) or Kvaesitso (its own thing, very search focused)
• Maps > Organic Maps (Open Source) and/or Magic Earth (THIS IS CLOSED SOURCE, I'm only recommending it in case you need traffic data in your map app since it's the one I see talked about the most as an alternative to Google Maps and Waze)
• Password Manager - Bitwarden or KeePassDX (I personally use Bitwarden)
• Reddit 🤢 > Stealth (Have no login, it's useful to keep track of the few stuff you might still want from there)
• Spotify > Spotube (Let's you use your Spotify account to login and import playlists, but uses Youtube as a backend for the music, the only downside being that sometimes it doesn't find the song if it has extremely low views, but you can usually correct that with a click on the change source button) - I linked the F-Droid version, but I recommend to set it up from Obtainium with GitHub as a source in case youtube fucks something up and it gets updated, which at best will take days to reach F-Droid.
• Weather > Breezy Weather

Also here's some useful apps I have been using that maybe you'll find useful:

• AniHyou - AniList client
• Birday - Birthday Manager
• Feeder - RSS client
• Goodtime - Pomodoro timer
• Hypatia - Real time malware scanner (might not be needed, but I rather be safe)
• KDE Connect - Connects your phone and PC, allowing to control music, share clipboard, share files and more on LAN
• MedTimer - Medicine reminder
• Openlib - Download eBooks from Anna's Archive
• Book's Story - eBook reader
• Openreads - Offline book tracker, also let's you review the books you read
• Racoon for Lemmy - Lemmy client, I used to use Eternity, but it had too many issues, this one has issues too, but it's actively developed. I also recommend this one to be installed with Obtainium instead of F-Droid.
• Scrambled Exif - Remove metadata from photos before sharing
• Seal - Video downloader

Lastly, apps I installed but didn't start using yet that might be useful too:

• Buckwheat - Budget manager
• Grit - ToDo list and Habit Tracker
• Moshidon - Mastodon client, I haven't used it because I haven't created a Mastodon account yet lol, but looks to be the best one I could find when I was searching a few days ago
• Noto - Note taking app
• trale - Body-weight tracking
• Wuxia Learn - Chinese learning app