I have the Note 10. In settings you can set which apps should always be in wide screen mode. For example, I want all my videos in YouTube to be full screen. But, I've noticed that I still have to expand them. Yes, I've restarted my phone. I've also noticed with messaging, I'd I set a number as default, each and every time I'm asked to st the default. Any suggestions?
YouTube expands to full screen without clipping the picture. This means that most videos are shown in 16:9. When the Note 10 is in landscape mode, this leaves the edges with black bars since the Note 10 screen is 19:9 ratio. If you expand the YouTube screen to eliminate those black bars, you will clip content off the top and bottom of the screen.
Sounds like you want the default to be "no black bars, clip the content off". I don't think that option is available.
When the 16:9 ration first starting to appear you saw a lot of TVs offer the "fill screen" option. I think that option has disappeared because people didn't want to lose content that was clipped off and the resulting pixelation from zooming the picture.