"It's weird because on the net the general consensus is to add fish right
away but in France the golden rule is to wait 1 month."

Similar consensus in Italy too and it is what my father used to do all
the time. The only difference with the method you stated is that we
add fish food every day during that month, it's no different to
fishless cycling really, the food quickly turns to ammonia and it
simulates a fish load in the same way as straight ammonia does. I
recently cycled my 90 gallon this way, took around 20 days. It's also
a good way to keep a tank cycled when you have no fish in it.

Giancarlo Podio