I’ve created a font from hardcopy manuals for a computer game. So this is a fan creation. Can I apply the OFL to it?
There are two issues here:
Permission to use the graphic design of the hardcopy manual to create a font based on it. Since that hardcopy manual (and internal artwork) is likely to be copyrighted by the original author you may need their permission. That would be the case whether you are creating a font for release under the OFL or for commercial sale.
If you get permission, the process of applying the OFL. That process is outlined in the OFL-FAQ question 4.2.
Hope that helps!