firstly, thank you for the 4:3 fix in android app , I've now configured steamlink in the android app to cap to the 1280x960 resolution of the client device (ayaneo pocket air mini)

issues:
1: first start to steam big picture from 4:3 device it will be 16:9 image and games launch as such, navigating to the remote play- host streaming options on the PC and selecting resolution to match client, will then break big picture mode image, cutting off most the image on PC and client, this is a first time setup bug- once the remote play stream is ended and started fresh with this setting already changed on PC host options, it correctly boots the remote session into 4:3 big picture mode

2: now big picture mode is in 4:3, launching a game that is 4:3 resolution supported ( Duke Nukem 3d world tour 20th anniversary edition ) and exiting the game to desktop from in game, will return to a 16:9 big picture mode, with no way to return to 4:3 unless restarting the steamlink session again.

expectations: for steam to remember resolution of client device in the session and display stream correctly when exiting games.

only way to retain 4:3 is to exit the game from steam Gamepad UI, NOT from any in game main menus.