Firstly is this thread relevant?

Secondly, if you have an opinion on this, make it known please. I'm looking for a practical way to save entity data. If you want to see my entity class, it's below. I'm looking to save the serum variable. What I have right now works fine but it does not save across world joins.

public abstract class Dinosaur extends Animal {
	
	static final EntityDataAccessor<Integer> serum = SynchedEntityData.defineId(Dinosaur.class, EntityDataSerializers.INT);
	
	protected Dinosaur(EntityType<? extends Animal> e, Level l) {
		super(e, l);
		
	}
	
	public boolean isJuvenile() {
		return this.isBaby() && this.getSerum() > 0;
	}
	
	@Override
	public void tick() {
		super.tick();
		
		if (this.getSerum() >= 4) {
			this.age = 0;
			if (this.isBaby()) {
				this.setBaby(false);
			}
		}
		else {
			if (!this.isBaby()) {
				this.setBaby(true);
			}
			this.age = -20;
		}
	}
	
	@Override
	public void defineSynchedData() {
		super.defineSynchedData();
		this.entityData.define(serum, 0);
	}
	
	public void addSerum() {
		int s = this.getSerum();
		s++;
		this.getEntityData().set(serum, s);
	}
	
	public int getSerum() {
		return this.getEntityData().get(serum);
	}

}

Override add/readAdditionalSaveData()