All Samsung Galaxy phones have a built in desktop OS called Dex. I remember plugging my monitor usb-c cable to charge my phone and being blown away when a desktop UI appeared on the monitor

DeX is very good, lot of fun to use with a lapdock. However, you need to check if the particular model of phone supports it. Usually it's the more expensive models, so Galaxy S, Galaxy Z Fold/Flip, Galaxy Tab S, and 1 single model of A series, the A90 5G.

https://www.samsung.com/us/support/answer/ANS10001955/

Works on my S21U. I use it a lot because I have some weird thing where I'll get really tense typing on a touchscreen keyboard, so if I have to type long messages in android-only apps its going on the docking station.

I used to love Dex, but later they removed the support for macOS. It used to work elegantly and android to mac connection was so easy. Being able to take calls, see messages and also file transfer. :)

that is pretty cool - wonder if it supports keyboard/mouse too ?

It does. And you can also use the phone screen as trackpad while in Dex mode. It's actually a pretty good desktop environment for Android.

Every iOS and android device supports mouse and keyboard at this point

It does.

You're probably thinking of https://www.cnet.com/reviews/motorola-laptop-dock-review/ or https://www.theverge.com/2015/10/6/9464639/microsoft-windows...

Nope, it was a Linux project.

Pinephone used to be able to do that a few years ago when I tried.

This was an Ubuntu phone concept back around 2011/2012. Steam Deck can do it, but you have to manually switch to desktop mode.

There was a company named "always innovating" around 2008ish which sold a hybrid of phone/tablet/laptop. Funnily enough, the website still exists [1].

[1] https://www.alwaysinnovating.com/products/smartbook.htm

Ubuntu had a kickstarter but it didn’t succeed.