But it is not simply a matter of that, first of all you must have legitimacy, or in any case you must have the strength to force an independence, even if it is illegal.

90% vote for independence, but the referendum participation was 43%, that means that more than half of the population, 57% of Catalans did not even attend the referendum.

The Austrian Anschluss on behalf of Hitler had a 99.73% approval, and it was found that the result was not manipulated, is it then legal?

The same happens with the annexation of Crimea by Russia, which violates the Ukrainian constitution, and the results are also very reliable.

To declare independence you must have a constitutional legal framework, or at least the strength of most people who really want to become independent.