I use portrait mode by default almost all the time - all the apps that are optimized for landscape already have an option to predefine "portrait or landscape" option in their settings.
Now, I use a SK for input in both portrait and landscape mode - depending on situation.
If my both hands are free, I swipe the notif bar, enable landscape, and then type the text (quicker).
If I am carrying something and I have only one hand free - I type in portrait mode.
Sometimes, while walking for example, I prefer 12key "ABC" input, so I long tap on input and choose the "samsung" keyboard, which I predefined as 12key input. This is because the portrait mode is too small, and the landscape is not ergonomic to type with one hand (or better - the phone dimensions are not optimized for 1 hand landscape

It would be really nice if there would be a settings option to "enable landscape while typing - for apps that have a landscape display option".
So:
the phone is in portrait mode.
I could open the message, tap the input field, the keyboard is shown, and as I rotate the phone, the app + keyboard are rotated also.
As soon as I exit the app (or hide the keyboard - if this is easier to encode), the display would "lock" back to portrait (as predefined).
I see some apps can be defined as display in "landscape" - but I don't want it all the time for the app in use - I want to be able to choose.
Anyway - Thank you for a wonderful keyboard

p.s. - there was few similar questions on forum, but I am talking about the apps that already have a landscape option
p.p.s. - please let me know if the smart keyboard already has this option and how to activate it - I started using it a while ago...