Cant I make a support forum as well?

I'm unsure of what you are asking for. If you are asking on how many installations you can make with a single license then you should read this from the pre-sales FAQ:

How many installations can I make with a single license?
Each license permits you to install the software once. However, you may create a single additional test installation for testing purposes only. Any test installation of this kind must be password protected, and access to it must be limited to you and your website staff.

Can multiple domains or subdomains be used with a single license?
Yes, as long as the domains or subdomains all resolve to the same installation, all of the content is available at every domain or subdomain, and there is no attempt to make them appear as separate installations.

Link: https://xenforo.com/community/threads/pre-sales-faq.4951/
 
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