Why the weird lag in Screen Sharing app when using the LG Ultrafine 5K monitor?
Apple's implementation of VNC ScreenSharing often falls short, with significant lag regardless of whether Adaptive Quality is selected or not. A more robust 3rd-party solution like (the free) VNCViewer will provide you with fine-grained compression control, allowing workable VNC sessions over the tightest of bandwidth (e.g. through a shell tunnel to a remote server with really low upload speeds).