I am a morderatly new user to the world of the Ubuntu MATE + Pi, but have a lot of experience with ubuntu MATE and the Raspberry Pi (seperately). I recently have been using steam link with the Raspberry Pi, and so I went about trying to install Steam Link. However, it said that steamlink was not found. I know for a fact it's supposed to install on ubuntu MATE, because I've read about it in their Raspberry Pi documentation.
I'm using 18.04, and have got the ARM64 version.