RPI is not capable to play game like fortnite, because it requires a lot of GPU, so PC or console are capable of playing them.

yes, you could use flight simulator on RPI-3, sim vim cockpit is a standalone program providing a set of realistic fully functional aircraft instruments.

there are number of websites that are hosted on PI, two of them are stated below:

http://dustinspi.ddns.net
http://pi.qcontinuum.com/

my first computer was Lenovo R61i laptop, which i purchased in 2008, it's specs were 2 gb ram, 80gb hard disk and intel celereon processor with windows 7.