If an organisation is asking you to submit an assignment in its very first round then just run in the opposite direction since they are most likely scouting for ideas and not looking to hire. In most cases it's just the HR being asked to do the sweet talking with zero intent. Sometimes even the co-founders (they're clueless, trust me) will reach out to you directly with an assignment in the very first conversation and will ghost you after receiving ideas.
If you have cleared multiple rounds where each peer/hiring manager has spent considerable time and are asking for an assignment, there is a good chance that your candidature is progressing, and it's worth giving it a shot. There's also a good chance the team members who interviewed you may like you in this process and you can still get through with an above average assignment.