A lot has been said, but I'll repeat a few.
- F-Droid (I use Droid-ify)
- Debloat it https://github.com/0x192/universal-android-debloater
- Change the launcher and icons (lots of choices, I use Lawnchair with Arcticons or Delta)
- Check out the different browsers
- Check out the different keyboards
- Get some key apps like Newpipe (or equivalent)
- If the phone isn't rooted, any changes can be reset by doing a factory reset, so you have nothing to lose but time.