The walls of the cell are made of crying obsidian. The entire cell is in the effective range of 6 elder guardians, which give MF3 at worst every minute. The entire cell is kicked every 2 hours to prevent breaking any obsidian. There is no wood in the cell so no pickaxes or crafting tables can be made. None of the decorations in the cell are enough to escape. Above the cell is a pearl glitching detector and a 3-high squilly trap to prevent squillying out.
More Security
Due to being entirely under the nether roof, it is impossible for outside players to enter the prison from above. The overworld is banned and has wither walls so portalling directly into the cell is impossible, the nether has 8 mob ban columns protected by wither walls, and there is obviously no need for a floor detector because of papermc.
