How to enable these unsupported web page

Or contact the Website owner and tell them to support your iPad's Safari browser too.

This is an error straight from the website. There's not much that can be done form your side, the website needs to support the iPad browser itself.

You can try to download Edge, Chrome or Firefox from the App Store onto your iPad, and see if that works.

The only way to access an unsupported website is to use one of the browsers mentioned in the screen shot.