Universal clipboard is pretty great too. It's another thing I wish was just an open standard that all the things supported, not just the Apple ecosystem.
Interestingly, it seems to present shared KBs and mice as physically connected devices. Any time I use Universal Control on a Mac I haven’t before the little keyboard identification assistant that opens when you directly plug in a keyboard pops up.
I sometimes need to work on mobile development, so on advice from a sibling comment I installed KDE Connect, and it's actually pretty great and does copy/paste and remote mouse/keyboard pretty well, but you do have to a) enter the app, b) select the device, c) then finally choose the thing you want to do. They've made it about as frictionless as possible, but it won't be the same as first-class OS-level support. e.g., I can just copy some text on my Mac, and paste it a second later on my iPhone, without any manual orchestration
[0] https://blog.pushbullet.com/2014/08/20/introducing-universal... [1] https://kdeconnect.kde.org/download.html
And operating systems could allow user to select their preferred server, although I wouldn't expect Apple to allow something advanced and anti-vendor-locking like that.