Using apps to fake GPS location, like Fake GPS, is not enough to trick some apps into thinking they are somewhere else.
One obvious thing to do is to use a VPN to spoof your ISP location as well, but there's more.
Apps also rely on the "Improve location accurary" that you can find on your Android settings. When that is turned on, geolocation also uses info about nearby wifi and cellular signals. If you turn that option off, the app will tell you it needs location info to work and will refuse to continue. As far as I know, there's no way to circumvent that without rooting the phone or running the app on an emulator.
One easy option, though, is that sometimes apps have equivalent versions running as web apps, and web apps cannot fetch location info as easily. If the app you're trying to use has a web version, just turn the VPN on and you should be able to use it just fine.
If you need to cast to Chromecast, it will probably not work unless you configure the VPN directly into your home router.