Seditious conspiracy typically involves an agreement between two or more people to forcibly oppose government authority or delay the execution of a law. Lawful protests might criticize the government or call for changes in policy, but do not advocate for, plan, or engage in violence or force against the government.
For example: Organizers planning a peaceful march to demand policymakers address climate change is lawful protesting, whereas plotting to attack infrastructure to force policy change would be seditious conspiracy.