Как работает сборщик мусора с объектами?

Ссылка на него останется в транзакции.

Fragment fragment = getSupportFragmentManager().findFragmentByTag(TAG_FRAGMENT);
if(fragment != null)
    getSupportFragmentManager().beginTransaction().remove(fragment).commit();

Что. Ты. Хочешь.

private val onNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
        val ft = supportFragmentManager.beginTransaction()
        var fragment: Fragment?

        when (item.itemId) {
            R.id.navigation_home -> {
                fragment = ListObjectsFragment()

                ft.replace(R.id.fragment_container, fragment, LIST_OBJECTS_FRAGMENT)
                ft.commit()

                return@OnNavigationItemSelectedListener true
            }
            R.id.navigation_person -> {
                fragment = ProfileFragment()

                ft.replace(R.id.fragment_container, fragment, PROFILE_FRAGMENT)
                ft.commit()

                return@OnNavigationItemSelectedListener true
            }
            R.id.navigation_store -> {
                fragment = ListTestsFragment()

                ft.replace(R.id.fragment_container, fragment, LIST_TEST_FRAGMENT)
                ft.commit()

                return@OnNavigationItemSelectedListener true
            }
            R.id.navigation_rating -> {
                fragment = RatingFragment()

                ft.replace(R.id.fragment_container, fragment, RATING_FRAGMENT)
                ft.commit()

                return@OnNavigationItemSelectedListener true
            }
        }
        false
    }