In our company, everyone works separately, and there is almost no team spirit. We tried to hold corporate parties, but it doesn't help.

I understand your problem, and it is very common in modern offices. Often the reason is not that people don't want to communicate, but that they simply don't have the opportunity to interact outside of work tasks. One of the best ways to bring a team together is to solve problems together in an unusual situation. That's why I recommend paying attention to real-life quests, such as the service https://boxroom.com/ . These are escape rooms where a group of people must work together to solve puzzles and get out of the room in 60 minutes. This experience greatly strengthens teamwork, teaches trust, role distribution, and interaction. After such events, even colleagues who previously hardly communicated begin to understand each other better, which has a positive effect on the working atmosphere.