MTL - Thrive in Catastrophe - Chapter 100 The builders of Fanwai (below)

The protagonist, a renowned gamer/YouTuber aka [TorchDancer] is a master of the game “Tril Trilo Trilogy.” When offered a chance to playtest the prequel, “Part 0,” he jumps at the opportunity. But a twist of fate plunges him into the game itself, transforming him into the series’ ultimate villain, Frank Wonderstein. Trapped in a monstrous body, he must navigate a dangerous world, unraveling the secrets of the game and his own destiny. Can a hero become a villain? Or can a villain find redemption? Well, you’ll just have to read to find out.

The world that nurtured the civilization which reached the pinnacle of magic was on the verge of destruction.
The last survivor transmigrated to the past, when the magic civilization started growing, as countless mages were still fumbling their ways through the thorny paths of magic knowledge.
He, who came from the end of the magic era, aim to reach the pinnacle of magic.

Betrayed by his former gang and thrown into the Rendhold Underprison, Dantes has spent the last five years scraping by. A whoreson of orcish, human, and elvish blood, he's lived on the periphery of the periphery, lying, cheating, and stealing to survive. After a run of bad luck, he's made a powerful enemy. Luckily, he's also gotten all the tools he needs to turn things around.A slow burn progression fantasy focused on rising through the criminal underworld of a city-state using newfound powers and quick wits.MC's powers will develop slowly, but he will use them in creative ways to get ahead, and in the meantime he's not above just braining someone with a club.Anti-hero/villainous MC with a code.

I got transmigrated into a game I’ve never seen before.

I thought it was a top-notch RPG and spent 30 years on it.

I retired as a war hero and planned to spend my remaining time leisurely.

But it turns out, it was an academy story?