I've never seen spaces used with a three workspace split across one window. I use space daily and I just looked into it, to see if I can enable anything similar to what's shown in the video, but it doesn't seem like it... I can only flip from one workspace to the other, not keep multiple workspaces open in one display. Can you provide any more detail? This would be a game changer for me
Turn off "Displays have separate spaces" and multiple displays will all scroll like in the video.
As for the three screens on one display, I speculate that is a special software feature of the monitor he's using. Some wide displays can treat portions of the screen as separate displays with their own video inputs. Or he set up each space manually split into three apps and then swipes between spaces. It's hard to see what display he's using.
Looking closer at the video, I think he’s got a MacBook Pro with three video cables coming out. Each is no doubt connected to separate display input. The monitor displays each on a separate section of the screen. He has “ Displays have separate spaces” turned off for sure.
I think this is the display. If it’s not, then it’s probably another Samsung with similar inputs.