Disappearing folders and files after migration on Mac Air

A couple of days ago, I did a migration from an old Mac Pro to a new Mac Air. The message saying that the process was completed appeared after almost three hours. The next day, I proceeded to erase the folders (e.g. 2015, 2016, etc. through 2024) with their files on the hard drive from the OLD mac. They still appeared just fine on the new one. Then this afternoon, I noticed folders had disappeared, and files were disappearing before my very eyes. Now, there is nothing left except for the titles of just a couple of the folders and subfolders, but the files are gone. I saw them in the iCloud.com recently deleted section and clicked on restore. They are grayed out on my computer but no files. What can I do?

[Re-Titled by Moderator]