What device do you have? Some cheap Android phones may have "advertisements" which can reinstall some apps after deletion, but you should be able to disable that
That’s normal for Samsung. They have had built in undeletable apps for years now. You can disable them but can’t delete them unless you root the phone.
It was one of the big reasons I switched away from Samsung to Pixel, and then eventually over to Apple entirely.
Fediverse data is open to basically anyone. This means while you're not gaining privacy you are de-commodifying all of it as well as your product use experiance.