In the video we are using a laptop dock as has been mentioned in this thread. It doesn’t have a CPU of its own, it’s essentially just a large battery, screen, keyboard, and mouse connected to an internal USB hub. When you connect the Librem 5 to it it uses the CPU on the Librem 5 but behaves like a laptop and charges your phone while it’s at it. Because they don’t have actual computer components inside they are a lot less expensive than a regular laptop.
While my work laptop needs a fair amount of resources, my personal laptop is something I just use for web browsing, email, writing documents, chatting, and watching videos. These are all things I can do just fine on the Librem 5 already and that’s why I plan on replacing my old original Librem 13 v1 with a Librem 5 + laptop dock. Having all of my files and applications and media (I use gpodder to sync up podcasts and vlogs) already there will be incredibly convenient.
I could see myself responding to a quick chat message or social media post in “phone mode” and then realizing that I need to type something a bit more extensive like an email or a forum post, which is always a pain on any touch screen keyboard, so then I’d connect to the laptop dock where I could type much more quickly and with a larger screen.