After reflection I will actually go on an NFT = one vote. The vote has a beneficial effect or not and it is the vote that will decide. A user who owns 51% of the project believes in it and it is not in his interest to vote against the proposal.

Yes, I understand. The goal is not to charge a fee or people won't want to vote. The goal being to be free on this part but to control the vote to the quantity of holder and not to the quantity of NFT possessed.

Yes but on my side I need a code solution without an external API. The comment below is more like I looking for

Thanks for your answer ! From this address, how can I read the JSON with all instructions inside the IDL ? Because idlBuffer return only a buffer, not a JSON readable IDL

So if I follow your advice, I do my instruction, then I do an await of getSignatureStatuses to make sure that the tx has landed on the chain (I guess the function waits to have a result ?) If fail, I start again, if success, I check then by recovering the transaction itself, and if in the meta I have no error then it's good, if not I also start again right ?