Why is there a delay on sound and video when using iMac 2009 as a monitor?

I have a Macbook Pro 2024 and an Imac 2009 that I connect with a mini displayport to usb c cable. It works, but: There is a delay in both picture and sound, that makes it almost useless. Does anyone here know how to solve this? Maybe it's just the way it is?

[Re-Titled by Moderator]