I used the Sunshine game streaming software and the WiiU homebrew port of Moonlight to get game streaming working on a WiiU gamepad. It’s sort of like a bootleg Steam Deck, and it works surprisingly well, but it mostly just made me want a Steam Deck.
It doesn’t need wifi though, PlayStation portal does. But yeah, the second screen was a questionable idea - too hard to implement in an interesting way, makes all local multiplayer games asymmetrical, makes porting difficult… Even Nintendo gave up
actually the gampad does need WiFi*, it’s just that the Wii U is the access point to its slightly non compliant WiFi ac network.
I mean connecting the console itself to WiFi, you are required to use the gamepad for most settings.
There’s no controller/wiimote fallback option.