Right, I posted yesterday about using an iPad as a 2nd monitor for nomads [1]. I understand a cheaper alternative is using a USB-C external display.
Not cheap though.
I have a 13-inch 2.5K monitor and its DPI is too for its size and macOS's fractional scaling doesn't work well. So I'm looking for better options.
There are also a variety of different attachment options, from no attaching to your machine (which I find preferable) to those that attach to your laptop and add two screens, one either side.
Watch out of fly-by-night kickstarter projects in this area, there have been a few in recent years including a monster that promised to add three monitors to your laptop (left, right, top) which I'm surprised people were taken in by (I found the extra weight of one less than convenient, even when sat at a desk, never mind three, hence currently using a stand-alone external screen).
There was an app for this back in 2010. I used it quite a bit when I was on the road with an original iPad.
Nearly 15 years later, Apple does it seamlessly and natively in iOS+macOS without any third-party apps is even better.
Dongle: https://astropad.com/product/lunadisplay/
First turns iPad into Wacom, second is a second screen with features Sidecar doesn't offer, such as reversing for use with teleprompter.
I was considering this, but wound up w/ a Wacom One for my MacBook, mostly since it uses the same stylus technology as all of my other devices (Galaxy Note 10+, Kindle Scribe, Samsung Galaxy Book 3 Pro 360).