I am surprised no one has mentioned the new Gnome sharing Extend feature[1]. It also uses RDP, but you enable it and it "just works," including input events from the remote device onto the virtual screen. I've used Synergy/Barrier/Waynergy for years, but this is a good way to add a screen anywhere that supports RDP (Android, ChromeOS, etc). My main reason to explore it is to extend to a nice high resolution OLED tablet. Latency is quite low, as long as you don't try to watch a high resolution video.

1. https://www.reddit.com/r/gnome/comments/uz5as7/gnome_has_mad... (discussion)