Those are just warnings. It should still install.
All it says is that it can't work out if it's enabled. Once it's installed, if the rewrites aren't working, that's a different issue to fix 🙂
Errors I get when installing
That looks like a PHP version problem
What version is the server running?
(and is it the latest Silverstripe version)
What version is your development machine running? What version is your server running?
There's likely to be a mismatch
How did you get the Silverstripe code? Did you use composer, or download the zip file?