If you are on Windows and have extra laptops of devices hanging around SpaceDesk https://www.spacedesk.net/ to a great free app (not open source). I use it with on my Windows Dev machine (WSL2 FTW) and use old laptops as external displays. It works well even on WiFI.
Thanks, I just got SpaceDesk working on a cheap Amazon tablet over USB-C (after realising I had to set PTP mode on the tablet...)
Should work really nicely as a second monitor when travelling, I have it on 60fps and high settings and the latency is barely perceptible.
I was excited seeing iOS 9.3+ on their requirements listing, but after digging my useless but 100% functional iPad 2 out of storage it won't install the app. :(
I do use the built-in iPad as a second screen thing in MacOS with a still supported iPad on occasion and that works quite well.
