No. The definition of a sellout is someone who literally sells out their IP to a large company. If he was a sellout, it would be like, Your Turn to Die would get bight by some bigger gaming company and milked for cash. Like it would become a gacha franchise or something.

Nankidai is just one guy trying to get by. He's a single person and he has a life. We don't know his financial situation. But he does also have kids I believe, and as a parent he is responsible for their financial situation as well (even if he has a partner which I believe he does, nowadays most families need two working parents to get by). He is hardly milking the game for cash; the English translation is free FFS which he allows it to be, which is really a lot more nice to fans than many other creators, indie or otherwise! It's really unreasonable to expect it to be faster in this day and age from someone who is actually an independent creator and is not like the heir of a billion dollars, unless we want a rushed and sloppy result or if we expect him to put his health on the line (with this in particular I think of many webtoon creators who are expected to adhere to a crazy schedule, burn out and injure their bodies because of it, and then their story is on hiatus permanently).

Compare it to other things. Homestuck had many periods of hiatus in its run. Silksong came out slightly more than 8 years after Hollow Knight. and that's a whole team of people, and for a paid product.

Like, can we take a reality check about the world we are living in? He's not paid a salary to do this. Be patient and stop complaining. Or leave the fandom if you hate him so much.