You will not find a single Venezuelan lawyer expert in Constitutional Law that thinks the National Constituent Assembly is legal. It was invoked by Maduro without a Yes/No referendum
Can you tell me the article of the Constitution that says you have to do a Yes/No referendum to call the election of the Constituent Assembly?
The Petro was approved by the Constituent Assembly, the highest institution in Venezuela, therefore the Petro was legally launched. The rest is gossip and desperate propaganda, unfortunately.