Full details here: https://www.informador.mx/mexico/Chocolate-del-Bienestar-en-ESTAS-tiendas-podras-comprarlo-20250710-0131.html

For reference, this is the legal definition in France (which still allows for some shitty chocolate BTW) :

Chocolat :

a) Désigne le produit obtenu à partir de produits de cacao et de sucres contenant, sous réserve du point b, pas moins de 35 % de matière sèche totale de cacao, dont pas moins de 18 % de beurre de cacao et pas moins de 14 % de cacao sec dégraissé.

Rough translation:
Chocolate is the product obtained from cocoa and sugars which shall contain no less (although see point b) than 35% of dry cocoa solids including 18% cocoa butter and 14% dry degreased cocoa.

Point b covers specialty chocolates, such as guanduja, etc.

Full text here(fr)

Edit: better formatting

50% is a little low for my taste. I wish it was more like 40 60 80. I'd be going for the 80. Or maybe just 50 & 70. I can live with 70.

so when do we see nestle/mars/whoever try to kill this?

I always wondered what darker chocolate would be like when first ingredient on the list isn't sugar... Powered milk is sweet by itself, but without all the sugar I think 50% cocoa content might be more powerful than in 50% chocolate we have here in Europe.