I’m not sure about the ability to boost the audio volume, but four different display modes are now available in version 2025.13.0: Letterbox, Original, Stretch, and Zoom.
They’re available during playback by pressing the vertical ellipsis menu, then Playback Options, and then setting the display mode. Letterbox appears to be the default (as it was in the legacy Android app).
[Edit]
I forgot to mention, the setting is persistent, at least in my testing. That is, if you set the display most to Stretch while playing a video, the next you play will also be in Stretch mode.
