How can the old 27-inch 5K iMac be used as a monitor for other devices? Runs at full 5K @ Anonymous184 with low enough delay

There are several replaced 27 '5K iMac 2020 in the company. The processor is Intel 8th generation or 10th generation i5. It is relatively slow to run the current macOS, but this 5K screen is still very cool. I am wondering how to use it to other devices (such as 24' 4.5 K M3 iMac) as an external monitor, the methods I have tried or found so far are not good enough 1. Use Apple's official AirPlay Server (which can be turned on in System Settings-General-AirDrop and Relay), the delay is visible to the naked eye, and when the iMac connected to the keyboard and mouse used for screen projection moves, it will exit as soon as there is an action 2. Connect the output of the source device through the video capture card, and then use the playback software to display the signal of the video capture card on the iMac used for screen projection. After searching for the capture cards sold online, most of them can only input the specifications of 4K @ Anonymous184, which is still a waste of the iMac's 27-inch 5K screen. Searching on Google in English, many people recommend Luna Display, an integrated software and hardware solution. Looking at his official website, mac-to-mac can only reach up to 5K @ Anonymous3190, and the delay is unknown Finally, I complained about Apple's various restrictions. With such a good screen and a set of software and hardware, it can be used as an output device. The current Studio Display and XDR Display seem to have chips running out of the system, but since iMac 2014, the Target Display Mode was cancelled to cut off the possibility of direct connection to the video output cable