Our company has a birthday party? But I don't want to be involved. What's the matter?

If you don't attend, it will make people feel that you are unsociable, but it doesn't matter if you are new here. Everyone doesn't know you and won't say anything. Besides, some people don't like this occasion. You can say that you have something to attend, or you can go and have a look. After a while, you can leave on the pretext that you are bored.