How do forums detect multiple accounts?

For educational purposes. This is a forum/site about cyber security. I think it will not be a problem for you.

I know;
cookies
browser fingerprinting
IP adress matching

But I learned that there are more advanced systems.
Like MaxMind. It calculates all the IP addresses that the internet service provider in my area can give me.

Do you know of any other systems they use?

How can this be prevented?
Obfuscated VPN’s?
Residental SOCKS5 proxies? etc. I want to get information. Thanks.