okay but that's all back-end. I actually have an example like this!

okay, so, if im playing an old DRM'd game I have on my desktop, and want to switch to my steam deck, I can do that.

but the interface that works on my steam deck (controller with touch pad, but no keyboard) is maddening to use on my desktop. I know, because I tried it once-steam calls it 'big picture mode' and it feels like being crippled when I use it on a computer with a full keyboard and mouse.

but I pick up the deck, and it's nice. it functions, its interface is pretty close to perfect. and if I tried to use either of those on my phone, i would take a train up to washington and fucking beat a valve employee to death with it.

what you're talking about is back end interoperability. totally unrelated, and I agree it's good! also, doesn't really exist anywhere near as much as it should, but that's sort of a different problem. see, each of those platforms has different affordances and design conventions. now, you can run compatibility and seamless use, so the video just appears where you want it. I actually have a slightly janky (but best I've found) version of that set up on my LAN.

but I would like to be able to click around and take a broader view of the incoming shit on my desktop with multiple 4k monitors. i absolutely need gesture support on my tablet, and on my phone I need gesture support, plus ABSOLUTELY DO NOT have space to display multiple things at once.

I don't need hamburger menus on my fucking desktop. I got space, and my cursor is precise enough the 90s/00's are the best we've done with UX in that space (because we stopped trying as soon as the iphone dropped). having ONLY ONE THING displayed at once on my desktop is fucking annoying. I have 7680 horizontal pixels over a few feet of space on my desktop, no one thing takes up that much fucking space, nor should it, and I like the ability to click and drag shit from different apps and move shit around and do all that good crap. it's great! and on my phone or tablet, that doesn't really work. I should be able to click and drag to my tablet, if I want to set that up (my tablet is air gapped because that's easier than degoogling and I mostly read+music on it) but my tablet needs a totally different interface, and anything that DOES work for my tablet, where im only ever really doing one thing I need to look at at once, is going to be frustrating as hell on my desktop.