Sync with other devices

My main computer was my 2019 iMac for years and I synced my Apple devices to it. I now use my 2021 MacBook Pro more and would like to sync my devices to it. I have no problem syncing my iPad, iPhone 8 Plus, iPhone 15 Pro to my MBP, but cannot change the iMac so that is syncs with the MacBook Pro. It keeps changing everything on my laptop! I was able to stop the other devices from the sync with the iMac, but am having problems with the MacBook. I am syncing all to iCloud which helps some except the good old iMac wants to be in control! All of my devices are up to date with Sonoma.