Mirroring Screen with Macbook and iMac?

Hello,

I am trying to use my 2019 iMac as a second monitor to my 2018 Macbook Pro. After finding out about Apple's Sidecar car feature to use the iPad as a second monitor, I tried seeing if somehow I can use Sidecar with an iMac but I believe it is only for iPad. I tried connecting my Macbook to my iMac every way possible, but it seems like there is no way to use the latest version of iMac as a secondary monitor. Are there any suggestions of how I can achieve this?

Thank you for your assistance.