Also, my antivirus program has expired and I'm wondering if I can play fortnite without the antivirus program without getting a virus. In a nutshell, I'm just wondering if it's caused by viruses
If you wash your hands and keyboard regularly, you probably will not.
As far as malware is concerned, you are relatively sure how you do not get the idea to download any data from an insecure source, such as chats linked to chats or the like.
The actual games are comparatively safe.
Fortnite definitely does not create viruses. It just does not work that way.
Whether a virus will infiltrate your system through a security hole in the game is another question.
Viruses do not emerge, they are smuggled into your computer from hacked or otherwise infected websites. Of course, this can also happen with programs, but with something like Fortnite, a hacker would first have to "infect" this server of the operator.
The danger is of course not 0, as well as generally when visiting actually reputable sites, but very low. In addition, the virus protection of Windows 10 is now so good that an additional anti-virus program no longer has to be so essential.