Missing data on new iMac after Wi-Fi migration

There is a clue in the other question you posted: iMac migration: Will old Safari data overwrite new? - Apple Community

In addition to the presence of "Bitdefender" as a complicating factor, you wrote you are migrating from a Sierra system to (presumably) Golden Gate. Using Migration Assistant is definitely the correct way to transfer information from an older Mac to its replacement, but the older a system is the greater the likelihood for error.

Going from Sierra to GG is a big leap — ten operating systems. There is absolutely nothing wrong with that, and you definitely don't need to upgrade macOS with every new release either. Having said that, Apple subjects Migration Assistant to rigorous testing for compatibility with only the past few operating systems. Exactly how many is not known but it is nearly certain they do not go back as far as Sierra.

Wi-Fi is not a concern in this case, otherwise MA would not have finished. A wired connection between the two Macs is always preferable, as well as a directly connected Time Machine backup drive, as they avoid the vagaries of wireless communication, but I do not believe it's worth the effort to start all over again with a wired connection.

Look for a "Relocated Items" folder on the new Mac: If a Relocated Items folder appears on your Mac after upgrading macOS - Apple Support

"The PDF document in the Relocated Items folder explains what to do with files placed in this folder."

If you were to describe the information (data) that appears to be missing, alternatives for manually transferring that data can be proposed.

Lastly, don't forget that Apple provides complimentary one-on-one phone or chat assistance as a service included with purchasing a new Mac. You should have received an email about it, but if not, contact Apple using the Support link on these pages. I encourage you to take advantage of it. I do. Even if I don't have anything in particular to ask them, I often learn something.

Did you migrate during the initial setup or using migration assistant after setting up the new iMac..?

If it was the later, then I would look for that migrated data in a second user account.

If done correctly all your data should be there. That being said I would not use wifi to migrate. Use a TM backup of your old Mac and migrate that file(s) to your new Mac with cable connection. I have done that many times and all the data files are transferred and in their correct folders.

tbirdvet wrote:

If done correctly all your data should be there. That being said I would not use wifi to migrate. Use a TM backup of your old Mac and migrate that file(s) to your new Mac with cable connection. I have done that many times and all the data files are transferred and in their correct folders.