If I ever get into prison, gambling will be the last thing I would do there. I will do my best to find a less stressful time killer and entertainment.
This prison gambling usually just fictional since they are well monitored on the CCTV by police while they are not allowed to hold money and other valuable things in the prison most importantly any gambling materials.
Most of the prisoners do task depending on the country. So it’s very rare for prisoners to have allowed time to gamble among prisoners.
Maybe other games such as sports is possible in prison.