As an oldtimer (Gen-X), I can't even with that mode of use. My thumb (is that what you use?) cramps up when trying to do that even a little.. I guess 30+ years of typing will do that.. The best I've done one-handed is type in my pin and launch an app and click an icon or two.

As it is, I hold my S21 with left hand, type with index finger of right - it's abysmal in terms of performance, but it's all I got.. landscape with both thumbs is usually worse because of such little lookahead / lookbehind - I can barely read the line I'm typing on - and fat thumbs. My kids do it all the time, but, well, their little girlish fingers (they are female) seem to manage it and they're quite quick at it.

My favorite phone (at least in terms of idea, execution wasn't perfect) was the Motorola Photon Q - full-size with slide-out keyboard. At least I could somewhat type quickly even if the keyboard wasn't great. Alas, 2012..

With a newish phone? I can probably type 10-20x as fast on my MS Natural keyboard (only one I can use for more than 30-40 minutes without RSI getting bad).. No wonder I don't "live on my phone" - I use it when necessary, and prefer my 40"+ 4K screen + real keyboard.