an app that can make your ipad or android a second monitor for linux, not mirrored, real extended display, can be use wired, or wireless via Wi-Fi, read the docs for installation guide, and open an issue, if there's any!
https://github.com/JamesLunaa/view-dock.git
GitHubGitHub - JamesLunaa/view-dock: Turn a Tablet or Phone into a real extended display for Arch x11 platform over Wi-Fi or USBTurn a Tablet or Phone into a real extended display for Arch x11 platform over Wi-Fi or USB - JamesLunaa/view-dock