And then such guy gets fired after probationary, because he does not fit the team. I would instead talk with colleagues about crypto and gambling, if they talk about that, but give general information, nothing that can show that I am good at them. Being silent and secretive also does not work well. As an employee, it is recommended to follow what you post or interact with in social media. A person might be a good and hardworking guy, fits well in team, but posts that he is radically against or support something, and employer can take that information as a reason to fire him.
If crypto and gambling are topics that people can comfortably discuss with each other then there is no reason why we shouldn't participate, especially when we are new employees needing to integrate. But if cryptocurrency and gambling are taboo topics in the company, then even if former colleagues talk about it, we should not engage in that conversation.
As a new employee, we should focus more on work instead of spending time gossiping, especially during working hours. There are always stories of old employees bullying new employees at work, so try to get along with everyone but also be cautious because we don't know their true intentions and what they will do to us. Just because they smile and talk to us doesn't mean they consider us colleagues and won't try to harm us.