I've got a Lenovo Yoga Tab 13 (https://www.amazon.de/Lenovo-2160x1350-WideView-Tablet-PC-Sn...) for "development" purposes. It's a nice tablet with 2k screen and enough power for pretty much everything, Android 13 and the killer feature for me: a micro-HDMI input. It works like a charm with MacOs/Linux as a second screen, but you can also connect a Switch or SteamDeck, grab a controller and you can play everywhere on a 13' screen.
The iPad and Mac have Sidecar which lets you use the iPad wired/wirelessly as an additional display for the Mac but it's so damn flaky that I gave up and got the portable monitor.
I do carry a cheap HDMI->USB adapter (Elgato Cam Link knock-off) which lets me use my Macbook as a monitor for things like Raspberry Pi's but not sure what the capture rate is.
