When use Actor::save and Actor::saveWithoutId to get NBT from a player, there is currect data of Abilities of this player showed below
However, ServerPlayer::load and Player::readAdditionalSaveData does not really read these data and write back to Player object
For example, when read NBT from a player in survival mode, change "mayfly" to 1 and use the function above to write back, the player still cannot fly. Actor::_sendDirtyActorData can't make it work eigher.
It is strange i think and wish BDS can have such abilities