Salt already answers the question itself at https://fiber.salt.ch/de... - it only talks about Android Mobile. This means that SALT does not provide an app for Android TV that uses a Mi-Box or other Android TV devices such as the Nvidia Shield, Sony Android TV, Philips Android TV, etc.

It may be possible via detours such as sideload, but this usually leads to operating or display problems that have to be solved with other apps. I therefore advise against buying the Mi-Box for SALT TV.

PS: By the way, the Playstore does not offer me the app for Android TV, only for my tablets or smartphones.