shiftscreen gives you a second screen for your iPad and iPhone. No more black bars when connecting your device to a monitor, instead place documents, websites and webapps on your external display. At the moment these are the supported webapps: Trello, Notion, Google Docs, Framer, Miro...
I think that’s one of the reasons Apple gave us full mouse support. The pieces are there, not saying it will be easy, but I think it is low-hanging fruit as far as sexy-new-feature for iPadOS 14.
It's also really bad for apps that don't do external screens properly for video. 16:9 within 4:3 within 16:9. So a small screen in the middle. I haven't used my Lightning to HDMI adaptor in a while to see if anyone is still doing it, but I had multiple apps that did the last time I tried. Almost as bad as the apps that block content going through the adaptor (downloaded videos on Google Play being my problem case, I won't buy anything from them until changed).